WHY: Political Power. Think of the Great Depression and the cure was WW II. FDR got us into that war, like the one before it, by violating U.S. Neutrality, hiding behind a neutral flag, while supplying only non-German powers with war and other materials. FDR was a fan-boy of Stalin and had a cabinet at least sympathetic and in some cases working FOR The Communist International ( re: Venona and Harry Dexter White as one example of many). The Soviet Union and communism in general was teetering on the brink of extinctionin the late 1930s, until we propped it up with American finances and industrial might. WW 2 was the greatest boon the Soviets ever had.
Consider today: poor economy, people waking-up to the political mismanagement of virtually every aspect of what shoud be our private lives: children, schools, and fogeign involvement in multiple wars, with no benefit for us as a nation. The looming 2024 elections, which 'They' will likely lose, if not again interfered with, would be a disaster for their power base.
In short; war provides emergency powers over virtually every aspect of a national life. If you're against Joe, then you're FOR the enemy. Just look at how They(tm) react to Tucker's interview with Vladimir Putin... Our 'reality' is manipulated to drive us like cattle, up the chute into the slaughter house.
Any trigger will do to start it. It won't have to be a real event either. Most of the wars we entered in the last 150 years were false triggers.
Sir John Honrybucket