At some point in history, the member states of the European Commonwealth (the Fallout universe's equivalent of the real-world European Union) had integrated into a single state-like entity; this was probably a federal union. (It is, however, not known which European states were members; the only confirmed member was the United Kingdom).
In 2052, Europe and the nations of the Commonwealth were heavily dependent on oil imports from the petroleum-rich states of the Middle East, and the Commonwealth nations responded with military action to rapidly rising oil prices that were damaging its economy, starting the terrible global conflicts that later historians simply lumped together as the Resource Wars.
A prequel to the Fallout series, Fallout: Resource Wars, set in a collapsing Europe (during the European Commonwealth's invasion of the Middle East), is one of the games that J.E. Sawyer would like to make if he could do any game, regardless of money and development time.