The Zimmerman Telegram was an important aspect of the American entry into the fighting of World War I. In fact, historians consider the Zimmerman Telegram to be an important factor that caused the United States to enter the First World War.
Bulgaria in World War I fought alongside the other Central Powers, including: Germany, Austria-Hungary and the Ottoman Empire. Its major battles were primarily focused in the Serbian Campaign of the First World War.
The Meuse-Argonne Offensive in World War I was a major event on the Western Front. In particular, it was especially important to the United States, since it is the second deadliest campaign in United States history, behind only the Normandy Invasion of World War II.
Australia in World War I played an important role in the overall war effort, across multiple regions. For instance, Australian soldiers fought in Europe, the Middle East and the Pacific region.
The Allied Powers of World War I included nations such as France, Russia and Britain, along with their numerous colonies. Together, the Allied Powers fought against the Central Powers in fronts across Europe and the Middle East.
There were several important American battles in World War I, including: the Battle of Château-Thierry, the Battle of Belleau Wood, the Battle of Saint-Mihiel and the Meuse–Argonne Offensive.
The Ottoman Empire in World War I was a member of the Central Powers along with Germany, Austria-Hungary and Bulgaria. Ottoman forces fought in several significant battles, including the Gallipoli Campaign.
Russia in World War I played an important role in the overall war effort. For instance, its armies fought along the Eastern Front of the First World War. Also, World War I impacted Russia as it was one of the factors that led to the events of the Russian Revolution in 1917.
Italy in World War I played an important role in the overall war effort for the Allied nations. For instance, Italian soldiers fought along the mountainous Italian Front.
Britain played an important role in World War I, and was one of the main Allied Powers of the war. It fought alongside its allies (France and Russia) against the Central Powers.