During World War I, the allies, Britain, France, the USA primarily fought against Germany and which two major forces?

While Germany was the industrial and military engine of the Central Powers, its two most significant partners were the sprawling, multi-ethnic Austro-Hungarian and Ottoman Empires. The conflict, in fact, was ignited by Austria-Hungary. The assassination of its heir, Archduke Franz Ferdinand (Review), by a Serbian nationalist in Sarajevo in June 1914 prompted the empire to declare war on Serbia, triggering a cascade of alliances that quickly engulfed the continent.

The Ottoman Empire, based in modern-day Turkey, joined the war a few months later. Often called the "Sick Man of Europe" due to its declining power, its entry was strategically vital. It controlled the Dardanelles strait, a crucial sea lane that the Allies needed to supply Russia. The Ottomans' involvement expanded the war dramatically, opening up new fronts in the Middle East (Mesopotamia and Palestine) and at Gallipoli. Together, these three empires formed the core of the Central Powers that fought the Allies for four years.