Nations go to war for a variety of reasons ranging from political, economical and more. Powerful countries can declare war over precious resources, such as oil. Motivation for war differs throughout history, but the range of impact war can have on a nation is just as vast.
For example, World War II bolstered the American economy, which was recovering from the Great Depression. According to About.com, after the war, many feared that returning soldiers would reclaim jobs and that citizens would be out of work. They also feared that military spending would drop, damaging both demand and available factory jobs.