America was initially neutral at the outset of World War 1. Even while the war raged in Europe, President Wilson actually tried to reduce the military budget as he had no intention of being dragged into the conflict.
However popular war mongers such as former President Theodore Roosevelt and various industrial and military elites argued that the United States should join the war and that it needed to be better prepared militarily. They advocated vastly increased military spending as well as a program of conscription and training of an officer corps.
In order to whip up public support for war, Roosevelt and his war loving associates organized the Preparedness Movement, which among other things held parades through out the country to raise public awareness and support. After all, every one loves a parade, and sending your sons and fathers to die on a foreign battlefield is so much easier to swallow when it is dressed up with flags and jolly marching music.
Unfortunate events such as the German sinking of the passenger liner Lusitania increased the public’s demand for war, and the Preparedeness Movement grew. President Wilson was eventually forced to agree to some of their demands and gear the country up for war, which eventually came for the United States, in 1917.