A war does not finance it self, it is your money that pays for it!
The US government paid for the World War I with raised taxes and liberty bonds.
The war started and all of its bills were flooding in but where did the money that paid for the war come from? There were two things the government could do. First, raise the taxes and secondly, borrow from the public.
Economists at that time thought that raising the taxes was the best choice. They were following traditions that stretched back to Adam Smith time, around 1776, who thought that raising taxes was the most logical thing to do in order to convey the actual cost of the war to the public. Oliver Morton Sprague, who was one of the leading economists at that time, argued against borrowing money from the public; he thought that it was wrong for young men to join the army and then, when they got back home again, pay higher taxes in order to fund the principal and interest of the so called war bonds.William Gibbs McAdoo who was the Treasury secretary at that time thought that there needed to be a balance between war bonds and higher taxes, so his idea was, very logical, to split them: 50% each, If it was more from higher taxes; the wealthier classes would be angry and withdraw their support.
The change of the taxes happened in October 1917 under the “War Revenue Act”. The act increased the federal income tax and at the same time lowered the exemption. For example: If you earned an income of $20,000 dollars before the act, the tax rate were 2%. That tax on the exact same amount of money rose to 7%. If you had an income of $2,000,000 dollars the rate went from 15 % up to 67 %.
 Graph of the income taxes in USA from 1917 – 2007