Answer:
1. through taxes on income and certain goods
Explanation:
The tax income in United States is the source of funding for all government programs created by the US government. This include the cost of purchasing weapons, paying soldiers' salary, military's research/development, etc.
During war time, the U.S government tend to increase the amount of tax that the citizens have to pay and allocated them to the military's budget.
On top of that, they also often stopped the production of a certain good and ordered the companies to change their operation to produce military's-related goods rather than their usual products. For example, during world war II many companies who produce agricultural machines were ordered to made parts for planes and tanks instead.