The Greek-Yugoslav confederation or federation, or Balkan Union, was a political concept during World War II, sponsored by the United Kingdom and involving the Yugoslav government-in-exile and the Greek government-in-exile. The two governments signed an agreement pushing the proposal ahead, but it never got beyond the planning stage because of opposition from within the Yugoslav and the Greek governments, real world events, and the opposition of the Soviet Union. The proposal envisioned the creation of a confederation of Greece and Yugoslavia.