Other states

Republic of San Marino

• Entered the war: 3 June 1915 (declared war on Austria-Hungary)

Republic of Panama

• Entered the war: 7 April 1917 (declared war on Germany)
• 10 December 1917 – declared war on Austria-Hungary

Republic of Cuba

• Entered the war: 7 April 1917 (declared war on Germany)
• 16 December 1917 – declared war on Austria-Hungary

Kingdom of Greece

• Entered the war: 27 June 1917 (declared war on the Central Powers)

Kingdom of Siam (Thailand)

• Entered the war: 22 July 1917 (declared war on Germany)

Republic of Liberia

• Entered the war: 4 August 1917 (declared war on Germany)

Republic of Brazil

• Entered the war: 26 October 1917 (declared war on Germany)

Republic of Guatemala

• Entered the war: 23 April 1918 (declared war on Germany)

Republic of Nicaragua

• Entered the war: 8 May 1918 (declared war on Germany and Austria-Hungary)

Republic of Costa Rica

• Entered the war: 23 May 1918 (declared war on Germany)

Republic of Haiti

• Entered the war: 12 July 1918 (declared war on Germany)

Republic of Honduras

• Entered the war: 19 July 1918 (declared war on Germany)