March 8: Senate adopts Rule 22: allowing permitting a vote of cloture on petition of 16 Senators and the termination of debate on a vote of two-thirds of the Senators present and voting. From 1808 until 1917 debate could not be closed off. The rule was changed again in 1975 to allow closing debate on a vote of three-fourths of all Senators.
April 3: Sealed Train stops at Beloostov Station on the Russo-Finnish border.
April 6: U.S. Senate votes to enter the First World War 82 to 6; U.S. House of Representatives votes to enter the First World War 373 to 50.
April 18: Russian Foreign Minister Pavel Milyukov blunders when he issues diplomatic note to British and French governments announcing the intention of the Russian Provisional Government to annex territories of the Ottoman Empire. Russian public opinion swings against him and his government because of disgust at the idea of more imperialist war.