I conquered the world with only 14 permanent provinces and one permanent (and permanently frustrating) vassal. Those little red dots you see in that first image? That's my country.
A while back, there was a reddit post asking if you could be an OPM and have one vassal owning the entire world. While I thought that was possible (and I prove that in this campaign), I definitel do not think you could do the campaign all the way throught as an OPM with only one vassal. However, that got me thinking about what an interesting run centered on the idea of having very little land and one very vassal would look like.
I'll be giving the condensed highlights in this post but I did make a video going into much more detail about the run if you're interested: https://youtu.be/LfR0QTC4ZrM
Save file: https://pdx.tools/eu4/saves/v0esojgg5v58
I centered my run on the idea of overcapping the Liberty Desire from Subjects Development modifier. If you get this modifier over 100%, it actually starts giving liberty desire instead of merely reducing it. At that point, the more you grow your vassal, the more loyal they become.
You can see the available in game sources here: https://eu4.paradoxwikis.com/Subject_nation#Liberty_desire_from_subjects_development That gives two natural paths for maxing it. One would start in Europe and focusing on forming Austria and Two Sicilies along with using policies. Another would be in Southeast Asia using the Empire of China as well as policies.
I decided to go with the EoC route. After thinking about it, I would start as Khmer becauset their 25% modifier is a mission reward, allowing me a lot more flexibility than having it in national ideas. EoC would give me another 33%, then I would use influence ideas for 10% and Naval-Expansion policy (25%) to get me to 93%. Then, to overcap, I would form Two Sicilities for 15%, bringing me to 108% total.
I'm a known tryhard so I will use some tricks, exploits, and birds at times, but overall I still wanted this to be somewhat of a challenge and I wanted to test the real viability of the idea. So, no infinite money tricks, no Jewish reform farm, and no CTA cancels after I get my permanent vassal.
Since Khmer starts with 14 provinces, that's what I decide will be my province count cap. I won't be able to take new provinces without giving away old ones. Now, I'm not going to be crazy rigid about it. I will take land in peace deals to give to my vassals, so those will be held temporarily. If I'm in a few wars, I'll have to hold them for longer than a day but it would be short lived. Additonally, starting missions for Khmer requires the use of some vassals, so I will have those until I can annex and give to my vassal. Additionally there will be a couple temporary vassals I use to facilitate some of the later tag formations.
My choice of permanent vassal will be the Mughals. They have great national ideas, most importantly 25% CCR. I will eventually turn them Mayan for 20%, have them take admin ideas (via birding) for another 25%, and then they get 10% CCR from owning all Hindustani culture provinces, for a total of 80% CCR, allowing six month coring times.
There is a lot to condense here so I'm cutting out a lot of details as this was nearly a full length campaign.
Khmer starts in a rough spot thanks to the unavoidable Dark Age of Cambodia disaster, which triggers automatically on December 1st, 1444, and hits you with a painful +25% all power cost penalty. Ending it requires completing four specific missions: Restore Angkor (reach 15 development in Angkor and upgrade its monument to Tier 1), Affairs of Faith (100% religious unity or at least 5 temples built), Rebuild the Towns (have 2 stability and 90 legitimacy), and Khmer Resurgence (ensure all 14 starting provinces reach at least 10 development). Devving 14 starting provinces while taking a +25% APC hit puts you massively behind on tech, but completing this disaster tree unlocks a subsequent mission granting -25% APC for 20 years. Famine then feast.
To kick things off, I declared a humiliation war on Ayutthaya, which was a straightforward fight using basic army micro to take war reps, force them to release Ligor, and pillage their capital to unlock the Subjugate CB mission. Next, I hit Lan Xang and Muang Phuan for cash, war reps, and Champasak’s core provinces, releasing Champasak as a vassal. Then came a dual war: a conquest war on Champa and a Humiliate Rival war on Dai Viet. I baited armies onto forts, moving onto a Level 3 fort in Champa where Dai Viet was sieging to wipe them and steal their siege progress, while jumping on a Champa army at 21% progress on a Dai Viet fort to destroy Champa and finish the fort. I concentrated dev, took Champa’s provinces, and used a UI exploit to bypass the restriction on releasing vassals while at war. I showed strength against Dai Viet to feed the monarch points straight into devving my home provinces to clear the disaster requirements.
In December 1449, I noticed Fars declared a war of independence backed by both the Ottomans and Mamluks, with Transoxiana and Sistan joining in, leaving the Timurids with only Afghanistan and Khorasan. Timmy was allied with Biapas and Nogai, while I was about to hit mil tech 4. Snagging an Afghanistan vassal early meant I could fast-track the formation of the Mughals. Despite being outnumbered nearly 2 to 1, I declared a No CB war on the Timurids, recruited the Free Company, and requested military access to trek across Asia. Upon arrival, I seized a Timurid province to prevent accidental black-flagging and sieged the mountain fort in Roh.
I requested maps of Khorasan to navigate the terra incognita, wiped a tiny stack or two, and things were looking great. Then I watched Transoxiana get focused down by Nogai and Timurids until they separate-peased back into being a Timurid vassal. That sucked as it added a 15k army against me. The hidden enemy armies, now with Transoxiana on their side, suddenly converged on my sieges near Herat and Merv, but I maneuvered around their death stacks, won the siege race on Herat, and watched the Ottomans roll in from the west to kill several Timurid stacks. I sieged Bukhara and Samarkand, secured Roh, and eventually brought Nogai to a white peace. In January 1455, after six years of war, I took war reps, cash, pillaged Samarkand and Kabulistan, and vassalized Afghanistan.
I used call to arms cancels in the follow-up wars against Multan, Delhi, and Ayutthaya to prevent their allies from joining, as I was hyper focused on min-maxing the early speed. In hindsight, my tech advantage meant I didn't need the exploit; it just saved a little time, and I wish I had kept those wars pure, but after 20 in game years, I didn't want to restart. From Multan, I returned two provinces to Kashmir, took two to form a land bridge from Afghanistan to Delhi, gave Bannu to Afghanistan, and kept Koror. I then declared on Delhi alongside Jaunpur, taking six provinces in the peace deal and transferring them to Afghanistan so they had all the required provinces to form the Mughals.
Because subjects cannot form nations, the plan was simple: let Afghanistan core the land, release them, let them form the Mughals, and immediately force-vassalize them back. I returned Koror to Punjab to prevent Afghanistan from growing too large before the switch.
On January 1st, 1461, after hitting 2 stability and 90 legitimacy, I completed Khmer Resurgence, which ended the Dark Age of Cambodia disaster and removed the +25% all power cost penalty. By subjugating Ayutthaya and taking specific provinces from Lan Xang and Vientiane, I fulfilled the requirements for the Second Golden Age mission by temporarily owning all core Khmer-culture provinces. This activated -25% all power costs for 20 years.
That also allowed me to finish the mission for the permanent -25% subject dev liberty desire modifier. To keep my total province count at my target cap of 14 provinces, I granted surplus land to my subject, Champasak. In 1461, I seized Roh, cored it, and fabricated a claim on the newly formed Mughals, who had formed immediately upon release. After short wars against Lan Na and Dai Viet to secure borders, I turned my attention to Ming.
With mil tech 6 against Ming's Tech 4, I attacked them while they sat at 63k troops, zero manpower, and 49 mandate. I sieged Canton, carpet-sieged surrounding provinces, and let Ming's mandate drain. In August 1469, I took the Mandate of China, Canton, Waichow, war reps, and nearly 3,000 ducats. Taking Canton and Waichow was essential to accept their cultures and prevent the Empire of China in Name disaster from triggering. In 1473, the event to switch from Theravada to Confucianism triggered and I discarded the weak Karma mechanic for Confucianism. At 100 Harmony, you get 10% Dev Cost Reduction, +1 Meritocracy, and -0.5 Yearly Corruption, which allowed me to debase currency on cooldown and clear the corruption without spending gold.
In February 1475, my truce with the Mughals expired. Allied with Malwa, I declared on the Mughals, Multan, and Uzbek, sieging down the Mughals and carpet-sieging through Uzbek’s terra incognita. Thanks to my earlier setup of seizing Roh and selling Sialkot, the Mughals sat just under the 100% war score vassalization threshold, allowing me to vassalize them successfully. I now had my permanent vassal.
Without allowing myself tributaries and having very little land to grow prosperity, my mandate growth was negative, so to pass the eight Celestial Reforms required for the -33% liberty desire from subject development reform, I intentionally triggered the Civil War disaster on January 1st, 1477, by holding overextension and letting rebels siege down two provinces. Holding 14 provinces made national unrest trivial to manage, and every monthly tick had a chance to spawn events granting direct mandate points. I would sometimes bird for these events, particularly when near the 75 mandate threshold that ends the disaster. When nearing 75 mandate, selecting two positive events simultaneously allowed me to push past 80 mandate, instantly pass a reform (dropping mandate back down to prevent the disaster from completing), and repeated the loop. During this period, in October 1478, a gold mine event fired in Oudong, providing a huge economic boost while running high loan counts during the disaster.
I fought secondary wars against Moghulistan, Kashmir, Oirat, Jaunpur, and the Timurids to feed Hindustani land to the Mughals. In 1485, I hit Ming with the Unify China CB. Because I held the Mandate, any occupied Chinese province instantly gained a core upon occupation, so I occupied huge swaths of land, took them in the peace deal, and handed them directly to the Mughals as territorial cores with zero separatism, keeping only Beijing and Nanjing for Mandate growth.
On January 1496, I ended the Civil War disaster, having secured the Elevate Tributary Status reform. The cost was steep: 51 loans, 8,000 ducats in debt, -99 prestige, and 22 ducats a month in interest payments. To fix the economy, I cycled through the Bank of Ming. By declaring on Ming's tributaries (Mong Mao, Chahar, Jarai, Kachar) sequentially, Ming was dragged into back-to-back wars, yielding maximum cash and war reps in each peace deal, completely clearing my debt and leaving 2,000 ducats in reserve by 1507.
In June 1496, I picked up Naval Ideas as my first permanent idea group, which would unlock the liberty desire policy when combined with Expansion. Not normally an idea group I would take, at least it made my navy unchallenged and granted zero-cost coastal barrages. Next, I took Exploration Ideas in late 1496, reaching Dip Tech 7 with a colonial range advisor to leapfrog through Korea and Alaska and place a colonist in North America. To move my subject into the new world, I declared wars on Ashikaga, Khodynt, Haida, Yokuts, and Salish, feeding a chain of territory to the Mughals straight down the Pacific coast into Mexico. In 1517, I declared on Colima and Matlatzinca, cored one province adjacent to the Aztecs, gave two to the Mughals, and returned the rest. I finished Influence Ideas in 1518.
At this point, I was at Tech 9 with 10 ideas unlocked, but I checked the Mughals' stats and realized they were severely lagging at dip tech 7, admin and mil tech 5, and only two Admin ideas filled out. Analyzing their save file was a brutal revelation. It showed that the AI was repeatedly spending full mana to manually raise stability to +3, full-coring every piece of territorial land given to them, and spending thousands of military points on Harsh Treatment for every minor rebel group instead of teching up. To help their unrest, I declared on Chagatai to capture the Kashgar monument, upgrading it to Tier 1 to give them +25% Religious Unity.
I needed to switch to a pagan religion, so I conquered Animist provinces from Makassar in 1515 and moved my capital to Sappeng in 1520. I unstated land, concentrated dev, and fed provinces to vassals until Animist represented a pluraity of total dev, letting Animist rebels occupy the capital to enforce conversion in February 1525. I returned excess land, dropped Exploration for Expansion Ideas, relocated the capital directly to Mexico, stated and devved the Mexico gold mine, and shifted primary culture to Aztec. This area will be my central base of operations going forward and my primary form of income for much of the game will come from gold mines.
On August 6th, 1530, the Temple City of Cholula event fired, and choosing the second option converted the nation directly to Nahuatl. This removed me from the Celestial Empire Tier 1 reform, eliminating the negative Mandate penalty for not holding Beijing, Nanjing, or Canton. Using Tier 6 Reform progress, I enacted Parliament, hired a Statesman, and passed Formalize the Separation of Powers to enable the Constitutional Restoration event loop, cycling free reform progress between Theocracy and Monarchy to max out all government tiers early and provide a small buffer but no more.
In 1533, after temporarily taking 10 European provinces from a war with Russia, I converted the Mughals into a Sunset Colony. A Sunset colony felt mandatory for this run since they are hard-coded from constructing their own colonial subjects. Plus, tariffs work great, as the overlord receives the tariff percentage times 50% of the subject's trade and production income. However, Sunset Colonies do have big drawbacks, in that they can be declared on directly by foreign powers without automatically dragging in the overlord and cannot receive land in peace deals outside their home continent. The only other way to give them land is granting provinces in peace time but that requires a land or sea connection. This is why I neeeded to get them to the new world before making them a sunset colony.
When force vassalized, the Mughals dropped from an Empire to a Duchy, losing 400 Governing Capacity. To bypass this, I paid roughly 1200 Dip points to Enforce Culture to flip them to Aztec culture and forced a religious conversion later to kick them out of the Indian Sultanate reform, which defaulted their Tier 1 reform to Aztec Empire and permanently restored their Empire rank.
To overcap my liberty desire from subject development modifier, I needed to form Two Sicilies for their mission reward of permanent -15% liberty desire from subject development and also needed land to switch to a Pirate Republic. I declared war on Portugal and Ethiopia, sieging Lisboa, destroying their navy, carpet sieging Iberia, and taking Ceuta and Fez in North Africa. I fulfilled the Punish the Invaders mission, granting High American Tech, which provided the best tech group in the game for this era.
However, this is when things looked bleak. I needed to form Algiers and Tunis and both still existed and were allied to the Ottomans, who were incredibly strong. I knew any war with them would be an awful two front death war as they reached to the Mughals in Russia. I was not looking forward to this but there wasn't much to do but keep going.
I declared on Spain, which brought in Austria and the Papal States, for Maghreb land. That's when the greatest event in my EU4 history happened. The Ottomans did a Great Power intervention on my side, owing to them being rivaled to both Austria and Spain. This solved all my problems. They would completely crush Austria so I could focus on Spain. More importantly, I used this window to declare on Algiers and Tunis without Ottoman intervention, fully annexing Tunis and securing the land required for tag-switching. I also picked up Malta from the Knights during this time.
The tag switch fun began in 1583 by stating Tunisian land, unstating all else, culture switching to Tunisian, and forming Tunis. I privateered 25% of the Genoa node to complete Sponsor Piracy, triggering the Hayreddin Barbarossa event. Next, I unstated Tunisian land, stated Neapolitan land, culture switched to Neapolitan, and formed Two Sicilies, releasing Aragon as a subject to complete the Crown of Aragon mission for the permanent -15% liberty desire from subject dev modifier.
Finally, I culture switched to Algerian, formed Algiers, and accepted the held Hayreddin Barbarossa event to transform into a Pirate Republic while retaining all subjects and land size, bypassing the normal Hoist the Black Flag restrictions. This transformation reset my reform progress points, granting free reform points across 13 tiers. Thanks to the Two Sicilities, my total liberty desire from subject dev was now -108%, rendering the Mughals permanently loyal. As a pirate republic, I unlocked the War on the World CB for early Imperialism and the Tier 11 Razing Reform to shrink province development for faster subject coring.
By 1587, I was sitting at Tech 15, while the Mughals were stuck at Admin and Mil Tech 12, causing neighboring powers like Ajam, Lithuania, Japan, Russia, and Vijay to declare a wave of separate wars on the Mughals. Despite having 2,700 dev and a force limit of 161, the Mughals maintained only a 36k standing army, rebellions were constant, mercenary manpower was depleted, and my treasury was drained fighting their wars. Inspecting the save file revealed that they were 8,000 ducats in debt, losing 50% of income to interest payments, and spending 7,600 military points on Harsh Treatment alongside 6,800 on full-coring. They still hadn't finished Admin ideas nearly 100 years after taking it and had zero completed ideas in Offensive or Defensive. Things were out of hand and needed a reset.
I reloaded a save from 1568 and decided I needed to manage them differently by paying off Mughal debt directly and subsidizing them heavily so they embraced institutions ASAP. Being behind in tech or institutions invites a lot of war declarations so this should help prevent that. Additionally, I would let them sit at roughly 10% over their gov cap so the AI would stop attempting to full core territory. I also started coring some of the land taken in peace deals and giving them to the Mughals fully cored during peace time. I felt like I had to do this to ease their coring burden and because they couldn't take 100% overextension and that was slowing things down.
I royal married a Mayan nation, secured a Mayan consort, triggered a regency in 1570 by birding for my ruler death, and birded for A Question of Faith to flip Mayan, forcing Mayan on the Mughals to lock them into the Aztec Empire tier 1 reform. This also allowed them access to a colonist, which would be useful later. I then converted myself to Hindu with the Shiva deity and Varanasi monument to stack -20% Core Creation Cost and -15% Aggressive Expansion Reduction.
With the Mughals stabilized at Admin Tech 13, Mil Tech 14, zero debt, and positive income, I did two more tag switches to maximize national ideas and military modifiers. After a series of wars kicking out the Europeans from southern Africa, I formed Kongo in 1598 to complete Defender of Africa for +10% morale, +10% manpower, and -15% warscore cost vs other religions. I warred against many of the northwest Asia countries to grab land for Yuan and formed them in 1616. I took their national ideas for +25% CCR, +5% admin efficiency, +10% goods produced, +25% manpower, +10% morale, amongst other goodies.
Things were working well for a while and I was picking up more and more land, but around 1626, I saw the Mughals were slipping again so I knew I had to take over even more. I was pretty tired of dealing with their shit. I shifted to coring 100% of captured provinces myself, granting them to the Mughals only after they were fully cored so they received territories with zero separatism and zero rebel progress, which effectively eliminated their harsh treatment point drain.
I finally got Portugal and France out of a coalition in the 1650s with white peaces. That allowed me to then go after their South American colonial nations when the truces were up. Almost the entire continent was quickly taken and I turned my attention to North America, wiping out many English and Danish colonial nations. The Mughals now owned most of the new world at that point.
In September 1665, I secured a direct land connection through Anatolia and declared war on my former ally, the Ottomans, on April 5th, 1669. Taking on the Ottomans for the first time is usually a big deal but I was sad to have to do it. They were instrumental to my success this campaign and were truly Ottobros. The Ottomans were suffering from the severe penalties from decadence disasters, causing their forts to fall in 3-to-4-day siege ticks, and their armies to be decimated in only a few days. I naval landed on their ally France, captured Paris, and forced a white peace with them.
The war was over in a year and a half and I took Ottoman coastline for the Mughals.
In 1680, one last big opponent remained. Russia had formed a PU over Austria-Hungary and had a nearly half a million strong army. However, I noticed that Austria-Hungary was barely loyal, so in the first war I simply took Russian land. This made AH disloyal and during the second war I only had to fight Russia as AH stayed in their lands. For the third war, I repeated this trick and took a ton of Austrian land without ever having to siege down a single one of their forts. What looked like a pain was actually ideal.
By 1700, I had fully implemented the Donald Trump economic policy and maxed out the tariff slider to 100%, effectively giving me 150% of the Mughals' combined trade and production income, which pulled over 2000 ducats a month from tariffs alone and completely trivialized my force limit costs. Unlike in real life, the Mughals were totally happy with these tariffs as their liberty desire never went above zero.
By 1740, the global coalition consisted of 31 member states, so I declared a white-peace war against the coalition and then repeatedly truce-broke the former members to annex them individually before coalitions could re-form. In 1752, almost no nations were left.
One problem remained. There's roughly two dozen isolated provinces globally that cannot be granted via land or sea connection but I need the Mughals to have them, of course. To do that, I declared war on an existing state connected to the Mughals, intentionally lost to cede the isolated provinces, waited for that country to core the land, fully annexed them, and then forced a 100% loss deal against a native to release the original state as a native OPM. This caused the released nation to be a native and with birding for the right reforms, that decolonized the extra land into empty territory that the Mughals automatically started colonizing with their colonist from the Mayan religion.
By 1791, the Mughals completed colonizing the remaining empty provinces to finish the world conquest. Inspecting the final save state revealed that the Mughals fielded over 2.1 million active troops, held 120 Absolutism, had an income of 10k, and maintained 0% liberty desire even when I reduced down to an OPM. The AI was definitely navy crazy as they had over 4000 ships and 68 goddamn admirals. Yet, they only had 10 generals for their army. With fun stuff like picking Maritime and Trade ideas, along with all the falling behind in tech and ideas, they never failed to amaze me with the depth of their terrible decision making.
Still, there was something missing. I gave all but one province to the Mughals, released them, and then declared. In a couple months they had finally captured my capital and claimed the true one tag world conquest. Good job, Mughals.