Births on April 20

Kai Siegbahn, Swedish physicist and academic, Nobel Prize laureate (d. 2007)

Kai Manne Börje Siegbahn (20 April 1918 – 20 July 2007) was a Swedish physicist who was awarded the 1981 Nobel Prize in Physics.

3 Mar

World War I
Russia signs the Treaty of Brest-Litovsk, agreeing to withdraw from World War I, and conceding German control of the Baltic States, Belarus and Ukraine. It also conceded Turkish control of Ardahan, Kars and Batumi.
2 May

Chevrolet Motor Company
General Motors acquires the Chevrolet Motor Company of Delaware.
24 Jun

Montreal
First airmail service in Canada from Montreal to Toronto.
4 Jul

Nicholas II of Russia
Bolsheviks kill Tsar Nicholas II of Russia and his family (Julian calendar date).
9 Nov

Wilhelm II, German Emperor
Kaiser Wilhelm II of Germany abdicates after the German Revolution, and Germany is proclaimed a Republic.