United States declaration of war on Germany (1917)
The United States declared war on the German Empire on April 6, 1917. President Woodrow Wilson asked a special joint session of the United States Congress for a declaration of war on April 2, 1917, which passed in the Senate on the same day and then in the House of Representatives four days later on April 6.
Source: Wikipedia — United States declaration of war on Germany (1917) (CC BY-SA 4.0)