Liliʻuokalani was the last monarch of the Hawaiian Kingdom who reigned from 1891 to 1893. The only queen regnant of the Hawaiian Kingdom, Liliʻuokalani faced rebellion from her subjects, foreign residents, and United States citizens. The revolutionaries forced her to abdicate the throne and then formed the Republic of Hawaii, effectively overthrowing the 98-year-old monarchy.
2. Nicholas II
Nicholas II was the last Emperor of Russia. He reigned from 1894 until his abdication in 1917. The abdication ended Romanov dynastic rule and the Russian Provisional Government took over, ending the rule of Imperial Russia. Nicholas II of Russia and his family were executed by Bolshevik revolutionaries in 1918.
3. Constantine XI Palaiologos

4. Wilhelm II
Wilhelm II was the last German Emperor who reigned from 1888 until his abdication in 1918. His abdication, which was brought about by a series of German defeats in the First World War, brought an end to a three-hundred-year reign of the House of Hohenzollern. After his abdication, the monarchy was abolished and Germany was converted into a democratic state, which came to be known as the Weimar Republic.
Umberto II of Italy served as the last King of Italy. His reign lasted for 34 days from 9 May to 12 June 1946. After the decline of Benito Mussolini's regime, a referendum favoring the abolition of the monarchy was being prepared in Italy. At that time, King Victor Emmanuel III abdicated his throne in favor of his son Umberto II, hoping that his exit might save the monarchy. But the monarchy was abolished as the referendum was passed, declaring Italy a republic.