EU4 Guide: How Does Economic Base Work?

Europa Universalis 4 is all about expanding. You take control of a duchy, a kingdom, a republic, or any kind of state, and you navigate it through 400 years of history to a level of glory it has never seen before. In this quest for glory, vassals play a big role. They’re states that aren’t owned but are controlled by you. You can force countries to become a vassal, but you can also ask them. Convincing them is pretty difficult though, mainly through a single modifier: Economic Base. What does it do? Why is it so powerful, and how can you improve it? In short, how does economic base work in EU4? You’ll find all the answers in this guide.

Before diving deep into the mechanics of EU4, there are a couple of things to clear up. First, this guide is written for version 1.34.5 of EU4 and assumes you have all the DLCs installed. The guide features why vassals are useful, what an economic base exactly is, how it’s calculated, how you can improve it, and finally if the entire thing is even worth it. So let’s dig in!

If you’re here, I assume you’re looking to build quite the empire for yourself in EU4. So check out our handy guide with 10 tips!

Vassals Make the World Go Round

To veteran EU4 players, it won’t be shocking to point out that vassals are important in this game. The wiki defines vassals as “a semi-independent nation that owes allegiance to a country.” In return for you offering military protection, they help you fight in wars, pay you money, and most importantly, serve as one of the best vehicles for conquest.

France’s vassals give it efficient military and economic boosts in the early game.

10 years after first establishing vassalage, you can integrate your vassals into your nation itself. Provinces that you get from vassals won’t be as likely to revolt compared to provinces you straight-up conquered, and they become profitable much, much more quickly. So freeing vassals, expanding them, and then integrating them is a strategy you’ll often find in tutorials and playthroughs. Especially if vassals get cores on provinces you want to conquer. If they have a core, they can more easily conquer and administer them than you can. You can find a lot of how vassal-based core-conquest works in our Ottomans guide, where we use it to make quick work of the Mamluks.

I’m getting sidetracked. What’s important is that vassals increase your power. There are multiple ways to get them – either militarily or diplomatically. You can attack them, and if they’re small enough, force them into vassalage. However, they’ll be disloyal, especially at first, and you’ll have to spend some effort to appease them. Alternatively, you can ask them to become your vassal. Doing so will avoid war (wars are expensive) and save you the effort of appeasing a nation angry that you’ve subjugated it. There is a multitude of factors that determine whether a nation is willing to be vassalized by you. But one of the most important ones is the economic base.

What Even Is an Economic Base?

Economic base simply refers to how powerful your economy is. You’ll find that the modifier for accepting a vassalization request always talks about “compared to.” It compares the economic power of the requester nation to that of the nation that it wants to vassalize.

Yeah, that’s already getting a little bit intangible. So let’s go over to the example of Brittany and France. Brittany is a logical target for vassalization. It exclusively borders France (after you’ve kicked out England, anyway), it’s part of the same trade node, close to the capital, and sits on some wealthy land. Conquering it is expensive – it will cost a lot of administrative power to get it fully integrated. Vassalization is the superior option when it comes to Brittany. However, when you ask for vassalization, it blatantly refuses – almost exclusively on the basis that your economic base is relatively too small. Apparently, Brittany believes that its economy is powerful enough to stand on its own legs.

Brittany is very willing to ally with us, but our economic base prevents vassalization.

EU4 gives the following impossible formula to determine the economic base modifier.

This formula gives me nightmares of high school math.

Worry not, dear reader! I broke it down, so you don’t have to. There are a couple of things that are important to calculate your own economic base. That’s the development in your own provinces and those of your existing vassals, and the relative autonomy of those provinces. If there’s a province with 9 development, but it’s 10% autonomous, it will only count for 8.1 (90%). The same goes for the target nation. So, the more centralized and developed your country is, the higher your economic base. And the same goes for the nation you’re trying to vassalize.

So, How Can You Improve It?

Given that the economic base is your total development modified by your autonomy, there are two very simple ways to improve your economic base. You can either upgrade your total development or lower your autonomy. Ideally, you’d do both. Some provinces in France have over 10% autonomy at the start of the game, so you can lower the autonomy there. Some of your existing vassals have states with autonomy over 30%, so integrate those when you can and lower the autonomy. Sure, it may trigger a revolt or two, but sometimes, a little tough love is necessary.

The other option is increasing development. You should always develop since it brings many buffs with it. More administrative development means higher taxation, more diplomatic development means higher production, and more military development means more manpower. Alongside numerous other benefits. The fastest way to gain more development is through conquest. France just so happens to start with one of the best rapid early expansions in the game. As the English hold on France is collapsing, France gains an opportunity to retake all of the English provinces in continental Europe (except Calais). Taking all of Normandy and Aquitaine will boost your total development dramatically.

There’s another thing that you can do if you’re deadset on making the economic base strategy work. Since it’s the relative economic base that counts, you can destabilize the nation you seek influence over as well. The easiest way to do this is by enforcing the Pillage Capital war goal on them when you beat them in a war. This takes development away from their nation and adds it to yours. Although this should help significantly, doing this just comes down to taking a long way around, and finding a complex solution to a simple problem.

Is Improving Your Economic Base Worth It?

Here’s when this guide takes a bit of a sour tone. The answer, in the case of France and Brittany, is a resounding no. Although it’s great for your income and power to develop more and lower autonomy, overcoming a -79 relative economic base penalty to accepting diplomatic vassalization is not easy to overcome. A closer look at the formula shows us why.

Despite our growth, Brittany still staunchly refuses.

The development of Brittany counts as an inverse square root to that of France. For you, adding a single development counts as just +1 to the formula. Brittany’s development counts as a square. When it develops from 55 to 56, that’s not an increase of +1 in the formula, but an increase of 111. The odds aren’t in your favor here. Outdeveloping a nation with 55 development and 0% autonomy, as Brittany, is next to impossible at the start of the game. Even with all of Aquitaine and Normandy, adding over a hundred development to France, your economic base won’t even be close.

And aside from that. France gets a subjugation casus belli on Brittany, so you can just conquer them and turn them into a vassal in the first few years of the game. Trying to economically dominate a European nation as large as Brittany is just not worth it. Every single province they own exponentially increases their odds to refuse vassalization. But that’s not to say that Economic Base is useless in every situation.

France gets a subjugation war goal on Brittany. Here, the economic base approach is just slow.

In the colonial game, it can be a great way to deal with one province minors, or native states. For Russia, far eastern Siberian nations like Chukchi dwarf in comparison, and can easily be vassalized. When taking on the smaller tribes in the American continent, nations like Portugal, Castile, England, and France can use their superior economies to get a vassalization.

Economic base is worth improving for its own sake, or when trying to vassalize small tribes in the Americas.

As a rule, when you want to vassalize a nation and see a huge economic base difference, put the idea of diplomatic vassalization out of your head. As seen with France and Brittany, it’s practically impossible to overcome. Vassalize them through war, invest in increasing relations after, and continue your empire building as such. If you ask me, I see war as a last resort in EU4. But in cases like Brittany, it’s the last resort that turns out to be necessary if you want them inside your Empire.

I hope you found this guide for EU4 insightful! Don’t forget to check out our 10 tips for empire-building guide, and let me know your thoughts in the comments! See you in the next guide!