| June 28, 1914 | |
Archduke Franz Ferdinand of Austria shot to death in Sarajevo. |
| July 28, 1914 | |
Austria-Hungary declares war with Serbia. |
| August 2, 1914 | |
Germany declares war with Russia. |
| August 2, 1914 | |
Germany invades France. |
| August 3, 1914 | |
Germany declares war with France. |
| August 3, 1914 | |
Germany occupies Belgium, Luxembourg and Netherlands without declaration of war. |
| August 4, 1914 | |
Germany declares war with Belgium. |
| August 4, 1914 | |
The British Empire declares war with Germany. |
| August 5, 1914 | |
Montenegro declares war with Austria-Hungary. |
| August 6, 1914 | |
Austria-Hungary declares war with Russia. |
| August 6, 1914 | |
Serbia declares war with Germany. |
| August 8, 1914 | |
Montenegro declares war with Germany. |
| August 10, 1914 | |
France declares war with Austria-Hungary. |
| August 12, 1914 | |
The British Empire declares war with Austria-Hungary. |
| August 23, 1914 | |
Japan declares war with Germany. |
| August 25, 1914 | |
Japan declares war with Austria-Hungary. |
| August 28, 1914 | |
Austria-Hungary declares war with Belgium. |
| November 2, 1914 | |
Russia and Serbia declare war on the Ottoman Empire. |
| November 5, 1914 | |
France and the British Empire declare war on the Ottoman Empire. |
| May 23, 1915 | |
Italy declares war with Austria-Hungary. |
| June 3, 1915 | |
San Marino declares war with Austria-Hungary. |
| August 21, 1915 | |
Italy declares war with the Ottoman Empire. |
| October 14, 1915 | |
Bulgaria declares war with Serbia. |
| October 15, 1915 | |
The British Empire and Montenegro declare war with Bulgaria. |
| October 16, 1915 | |
France declares war with Bulgaria. |
| October 19, 1915 | |
Italy and Russia declare war with Bulgaria. |
| March 9, 1916 | |
Germany declares war with Portugal. |
| March 15, 1916 | |
Austria-Hungary declares war with Portugal. |
| August 27, 1916 | |
Romania declares war with Austria-Hungary. |
| August 28, 1916 | |
Germany declares war with Romania. |
| August 28, 1916 | |
Italy declares war with Germany. |
| August 30, 1916 | |
Bulgaria declares war with Romania. |
| August 30, 1916 | |
The Ottoman Empire declares war with Romania. |
| September 1, 1916 | |
Bulgaria declares war with Romania. |
| February 3, 1917 | |
The USA severs diplomatic relations with Germany. |
| March 14, 1917 | |
China severs relations with Germany. |
| April 6, 1917 | |
The USA declares war with Germany. |
| April 7, 1917 | |
Cuba declares war with Germany. |
| April 7, 1917 | |
Panama declares war with Germany. |
| April 8, 1917 | |
Austria-Hungary severs diplomatic relations with the USA. |
| April 10, 1917 | |
Bulgaria breaks diplomatic relations with the USA. |
| April 11, 1917 | |
Brazil severs relations with Germany. |
| April 13, 1917 | |
Bolivia severs relations with Germany. |
| April 23, 1917 | |
The Ottoman Empire severs relations with the USA. |
| April 28, 1917 | |
Guatemala severs relations with Germany. |
| May 18, 1917 | |
Honduras severs relations with Germany. |
| May 19, 1917 | |
Nicaragua severs relations with Germany. |
| June 18, 1917 | |
Haiti severs diplomatic relations with Germany. |
| June 27, 1917 | |
Greece declares war with Austria-Hungary, Bulgaria, Germany and the Ottoman Empire. |
| July 22, 1917 | |
Siam declares war with Germany and Austria-Hungary. |
| August 4, 1917 | |
Liberia severs diplomatic relations with Germany. |
| August 7, 1917 | |
Liberia declares war with Germany. |
| August 13, 1917 | |
China declares war with Germany and Austria-Hungary. |
| September 21, 1917 | |
Costa Rica severs relations with Germany. |
| October 5, 1917 | |
Peru severs relations with Germany. |
| October 7, 1917 | |
Uruguay severs relations with Germany. |
| October 26, 1917 | |
Brazil declares war with Germany. |
| November 2, 1917 | |
First US soldiers die in battle. |
| December 5, 1917 | |
Russia concludes an armistice with the Central Powers. |
| December 6, 1917 | |
Romania halts conflict with the Central Powers with the Truce of Foscani. |
| December 7, 1917 | |
The USA declares war with Austria-Hungary. |
| December 8, 1917 | |
Ecuador severs relations with Germany. |
| December 10, 1917 | |
Panama declares war with Austria-Hungary. |
| March 3, 1918 | |
The Treaty of Brest-Litovsk ends the war between Russia and the Central Powers. |
| March 5, 1918 | |
Romania capitulates to the Central Powers with an armistice. |
| April 22, 1918 | |
Guatemala declares war with Germany and Austria-Hungary. |
| May 7, 1918 | |
Nicaragua declares war with Austria-Hungary and Germany. |
| May 7, 1918 | |
Romania capitulates to the Central Powers by the Treaty of Bucharest. |
| May 23, 1918 | |
Costa Rica declares war with Germany. |
| July 12, 1918 | |
Haiti declares war with Germany. |
| July 22, 1918 | |
Honduras declares war with Germany. |
| September 29, 1918 | |
The Allies conclude an armistice with Bulgaria. |
| October 30, 1918 | |
The Allies conclude an armistice with the Ottoman Empire. |
| November 3, 1918 | |
The Allies conclude an armistice with the Austria-Hungary. |
| November 10, 1918 | |
Romania re-enters the war on the side of the Allies. |
| November 11, 1918 | |
The Allies conclude an armistice with Germany. |
| November 13, 1918 | |
Russia cancels the Treaty of Brest-Litovsk. |
| June 28, 1919 | |
The Peace Treaty of Versailles ends the war for Germany. |
| September 10, 1919 | |
Austria signs the Treaty of Saint Germain to end the war. |
| November 27, 1919 | |
Bulgaria signs the Treaty of Neuilly-sur-Seine to end the war. |
| June 4, 1920 | |
Hungary signs the Treaty of Trianon to end the war. |
| August 10, 1920 | |
The Ottoman Empire signs the Treaty of Sevres to end the war. |
| July 2, 1921 | |
The USA ends the war with Austria by a resolution of the US congress. |
| July 2, 1921 | |
The USA ends war with Germany by a resolution of the US congress. |
| July 2, 1921 | |
The USA ends war with Hungary by a resolution of the US congress. |
| August 24, 1921 | |
The United States and Austria sign Treaty of Vienna. |
| August 25, 1921 | |
The United States and Germany sign Treaty of Berlin. |
| August 29, 1921 | |
The United States and Hungary sign Treaty of Budapest. |
| July 24, 1923 | |
Treaty of Lausanne creates the nation of Turkey. |