When Europe went to war in 1914, America stayed aloof. But sympathy for Britain was strong among President Wilson and his cabinet. The German decision to declare unrestricted submarine warfare against American ships in the Atlantic led him to declare war against Germany. America's previously small army grew rapidly in 1917 and trained hard, taking the field in large numbers in 1918 under the leadership of General Pershing to forestall a German assault on the western front.