Empire Day, which was also referred to as Imperial Unity Day, was the day on which Sheev Palpatine proclaimed himself to be the Emperor of the initial Galactic Empire, thereby bringing the Clone Wars and the Republic to their conclusion in 19 BBY. From the following year onward, Empire Day was observed as a holiday to commemorate the anniversary of the ascension of the Empire. The holiday's celebrations featured a procession on various planets under Imperial control, the playing of the Imperial song, "Glory of the Empire," and the broadcast of footage showing Emperor Palpatine with a pair of Royal Guards at the Imperial Senate, although the footage was altered to present the Emperor as younger and more attractive than his actual appearance at the time of the speech. Attendance at these celebrations was mandatory. On Coruscant, the holiday served as the culmination of a week of celebrations known as Ascension Week.
Furthermore, it marked the birth date of Ezra Bridger, and occurred two days before Luke and Leia Skywalker's births on Polis Massa.
Unity Day also served as a celebration of the fellowship among the Empire's citizens. The event was marked by elaborate military parades, exhibiting the power of the Empire's army and navy. After the Battle of Hoth, the Rebel Alliance launched an assault on a Unity Day parade located on Bar'leth, a planet within the Galactic Core. This strike was a strategic move by the Alliance, carefully designed to avoid civilian casualties while being broadcast across the galaxy via the HoloNet; Alliance High Command hoped that these actions would attract additional allies to their struggling Rebellion.
The original Empire Day was a holiday within the British Empire, observed on May 24, which was the birthday of Queen Victoria. It has since been renamed "Commonwealth Day" in the United Kingdom and the Commonwealth of Nations. The Star Wars: Episode V The Empire Strikes Back premiere was held on May 20, 1980, in the British capital, London, and the name "Empire Day" was used in marketing for the event. As a premiere for a royal charity, Princess Margaret attended, and the event benefited children's charities.