Napoleon Bonaparte (le petit caporal) 11 April

Napoleon Bonaparte (le petit caporal) abdicated unconditionally, on 11 April 1814. Shortly thereafter, in the Treaty of Fontainebleau the victors (Britain, Russia, Prussia and Austria) exiled him to Elba. Napoleon escaped from Elba on 26 February 1815. When he returned to the mainland, King Louis XVIII sent troops to stop him. Napoleon simply got out of his carriage and walked up to the soldiers and said "If any man would like to shoot his emperor, he may do so". The army (340,000 men) decided that this was too difficult and decided instead to have another go at pan-European domination. Happily, Napoleon’s final 100 days ended by the (rubber?) boot of the Duke of Wellington and Gebhard Leberecht von Blücher at the Battle of Waterloo on 18 June 1815 after which Napoleon was exiled to St Helena, where he died (some say of arsenic poisoning). Sadly, Napoleon never said "not tonight Josephine"; however, his dying words were the more enigmatic but less quotable "France, the Army, head of the Army, Josephine."
Speaking of mad Emperors, on 11 April 1979 Ugandan dictator Idi Amin was deposed. Whether any of this is more important than the 1868 formation of the Benevolent and Protective order of Elks in New York by Englishman Charles Algernon Sidney Vivian, I leave to others to decide.