In August 1914, world leaders expected a quick victory, but instead a bloody stalemate set in. Millions of men and women died as armies battled each other and the elements along a system of trenches that stretched across northern France, Belgium and Germany. The stalemate would define the war for its duration, until an Allied breakthrough finally defeated Germany in 1918.

The Allied forces numbered 4 million, led by Britain with its own army of more than 2 million “poilus” and the additional troops from the British Commonwealth countries of Australia, New Zealand and India. Germany, meanwhile, had 11 million soldiers under arms.

No country wanted to be left alone if war broke out, so two major military alliances took hold. Russia, fearful of being hemmed in by Austria-Hungary and Germany, teamed up with France. And the German military, known as the Wehrmacht, was considered one of the best in the world due to its armament, training, discipline and fighting spirit.

Woodrow Wilson went before Congress on February 3 to announce that the United States had severd diplomatic relations with Germany. He warned Germany that if its submarines continued to attack U.S. ships, America would enter the war. But he declined to ask Congress for a declaration of war. The German high command hoped that the Kaiser would declare neutrality, which would cause morale to collapse among the people and reduce the likelihood of revolution at home. However, the allied submarines scored a series of victories against Japanese ships in the Pacific, and in October Germany called off its campaign of unrestricted submarine warfare.