Albert Einstein needed ten years to flesh out his special theory of relativity into a general theory of relativity, but when he finished, he changed our understanding of the nature of reality itself.
German East Africa stood strong against British attempts to capture the territory. The key to capturing the German colony was to contest German control of Lake Tanganyika.
Political instability and mounting foreign debts lead to US military intervention on the island of Hispaniola.
By the summer of 1915, both the Central Powers and the Allies were keen to get Bulgaria to join the war on their side. The Central Powers won the bidding war, and Bulgaria became the fourth (and last) member of the Central Powers.
By the spring of 1915, it was clear that the war would last for a long time and that it would be taking an economic toll on all the nations involved, and there would likely be political consequences as well. In Britain, the debate centered on whether the government was doing enough to support the French, and in particular, whether British soldiers were being supplied with enough artillery shells to get the job done.
In early 1915, with the Western Front in a stalemate, Winston Churchill becomes the leading voice behind a plan to do an end run around the Germans and knock the Turks out of the war.
In the spring of 1915, just before the sinking of Lusitania and in international women's conference aimed at ending the war through private diplomacy, Germany uses poison gas on the Western Front.
The sinking of Lusitania and the deaths of 128 Americans was a shock. While there was little support in the US for war against Germany, there was a strong feeling that *some* kind of response was necessary. It was up to Woodrow Wilson to figure out what that would be.
Germany searches for a way to break the British blockade; Britain looks for a decisive battle.