US was actively involved in the first world war for only nineteen months(April 1917 to November 1918) but it mobilized its economy at extraordinary levels. At least four million Americans served in the war and the economy supplied raw materials and munitions. The main reason for US entering the war was that it considered it more important to save its allies. The first step in economic mobilization was to increase the size of the army to increase the number of soldiers to one million, but in reality the number of Americans who served in the war was more that 4,000,000. With the increase in the number of soldiers the demand for guns and ammunition, means of transport, food and clothing also increased. All of these led to the increase in the federal spending. The federal spending increased form 477 million dollars in 1916 to 8,4501 million in 1918. So we can say that the reason for increase in federal spending in defense throughout late 1900's was the second world war.
