On what date did German reunification formally take effect after the Berlin Wall era?

German reunification formally took effect on 3 October 1990.

On that date, the German Democratic Republic joined the Federal Republic of Germany under the reunification arrangements agreed during 1990. The event ended the political division of Germany that had existed since the creation of the two German states in 1949.

The date is different from 9 November 1989, when the Berlin Wall opened and large-scale crossings began. The Wall’s opening accelerated political change, but it did not itself legally reunify Germany. Reunification required negotiations between the two German governments, the four wartime Allied powers, and other international participants.

The Treaty on the Final Settlement with Respect to Germany, commonly called the Two Plus Four Treaty, restored full sovereignty to united Germany. German Unity Day is celebrated annually on 3 October as the national holiday of modern Germany.