The European Union started as a collection of European Nations that wanted to form a political and economic alliance for their common welfare, this was also called the European Union. The European Union continued to expand until most of the countries in Europe were part of the Union.
While in the late 20th and early 21st century the European Union was a loose alliance, the formation of the New Soviet Union started a chain of events that caused the Federalization of the European Union. The First of these events was the Second Red Scare, which caused Ukraine, Belarus and Romania join the European Union. This rapid joining caused the European Cession Wars, where parts of the United Balkan States, Ukraine, and Romania on the coast of the Black Sea split away from their constituent countries and formally joined the New Soviet Union. This caused tension between the European Union and the New Soviet Union, but the European Union eventually let the territories join, since the wars started after referendums that passed and the constituent countries denied, putting them in the wrong.The European Cession Wars caused a massive Federalization of the European Union. This included a complete renovation of the legal and economic system of the Union, as well as the creation of the Federal States made the whole alliance act more as a single state, rather than a collection of many.
In 2047, with the formation of many of the Great Unifiers, most recently the Asian Alliance, the European Union passed the Concordia Act in July of 2047. The Act passed in favor with a vote of 97-8 and the European Federal Union officially formed July 14th, 2047. Shortly after this, Switzerland joined the European Union as a highly autonomous state.
Today, the European Union is arguably, the most influential and powerful nations out of the seven Great Unifers. They work wholeheartedly with the other members of the Terra Pact and are the biggest funder of Terraformed of Mars and the UNSA.