This type of silly, ignorant argument always annoys me. Neither Imperial Japan nor Nazi Germany had the slightest interest in conquering the United States. Even if they did want to invade and conquer the US, neither had the naval or other military resources to do so, even if they had not already greatly extended themselves. Once piece of the US that Japan could have actually taken was Hawaii after Pearl Harbor; they didn't even try. It was FDR who greatly desired war with Japan and Germany; Japan and Germany basically wanted the US to leave them alone; while they carried out their plans for regional conquest.
On the other hand, the Soviet Union was attempting to conquer us; through spy rings, through the CPUSA and it's multitude of front groups the Soviets controlled important unions that dominated key industries, they dominated elite universities, and had a great deal of control over the movie industry (and after the Soviet Union was attached by its former ally Nazi Germany, Hollywood churned out movies that built support for American entrance into the war), and placed their fellow travelers into key government positions; including those immediately around Roosevelt.
The US's actions during WWII greatly expanded the power and territory of our most dangerous enemies, and Pat is right to ask the question, "Was it worth it?"
Ignorant.