[@User] In this, the EU will be just one of many groups of humans who have a space agency capable of maintaining colonies. Basically the EU of the Event Horizon world works very similar to how the EU works today, except that they are responsible for the space agency centered in France, which is funded not just by France but all members of the European Union. Likewise, the American space agency is not just used and financed by the US, but also by Japan, Mexico and Israel. Essentially it's just groups of countries uniting under alliances to claim areas of the universe.

I haven't had the opportunity to read The Expanse series yet, though it's been recommended to me by a few people!

Edit: [@DeepestApology] Sorry, I seem to have missed your actual question last time around. The EU still isn't a centralized federation, but rather has taken on the role of becoming an alliance for nations that are individually too small to make an impact with regards to space colonization.