The Unification

The Unification is an event in Terran history which coincides with the proclamation of the First Commonwealth on the the 24th of November 2072. It is perceived as the symbolic first ever union of all humanity under a single banner. However, the Unification Wars lasted until 2084, and it is only then that all of Earth was united. It is the main national holiday of the Terran Federal Republic, and is celebrated annually on the 24th of November as Unity Day. 
It is closely associated but distinct from the Foundation, which is sometimes called the Second Unification. The Foundation marks the official formation of the Terran Federal Republic and thus the Terran state largely as it exists today, on January 1st 2097.