CZARIST DEMISE (March): More than 300 years of Czarist rule in Russia comes to an end when Czar Nicholas II abdicates his throne. A provisional government is established but grows increasingly ineffective as the year wears on. On Nov. 7, Communist Bolsheviks led by Vladimir Lenin stage a bloodless coup in Petrograd (St. Petersburg) and topple the government.

NEW U.S. PORT (March 2): The Jones Act makes Puerto Rico a U.S. territory and Puerto Ricans U.S. citizens.

U.S. ENTERS WAR (April 2): German actions force the United States into the war. In January, Germany had announced unrestricted submarine warfare, going back on its pledge to warn neutral ships before firing. Under this policy, Germans blew up three U.S. ships. The British also intercepted German messages promising Mexico its U.S.-claimed land back if it helped to defeat the United States.

PATRIOTIC FERVOR (April 6): Inspired by news that the United States had declared war on Germany, song-and-dance man George M. Cohan composes his popular patriotic ditty, "Over There."

MATA HARI'S END (Oct. 15): A Dutch-Javanese courtesan and exotic dancer known as Mata Hari, Javanese for "Eye of the Morning," is executed by a firing squad at the Vincennes Barracks in Paris. Mata Hari, born as Gertrud Margarete Zelle, was convicted of spying for the Germans.

JEWISH HOMELAND (Nov. 2): The Balfour Declaration, saying that Britain favors "the establishment in Palestine of a national home for the Jewish people," is issued by Foreign Secretary Arthur Balfour, as British troops invade Palestine and seize it from the Ottoman Turks who have held it since 1516.

PROHIBITION (Dec. 18): The 18th Amendment, outlawing the transportation and sale of alcoholic beverages, is approved by U.S. Congress and submitted to the states for ratification. It is the only constitutional amendment to have a time limit for ratification -- seven years -- and the only one to be repealed.