You assume there would have been combat with Nazi Germany in the short run. I disagree. Indeed, but for Roosevelt’s belligerence in word and action, and his attempts to lure hitler into giving him a casus belli in 1940 and 1941, Germany may well have not declared war on the United States oin December 11th, 1941, since the Tripartite Pact was defensive only.
As to the premise that we could not have defeated Japan earlier than 1945, several salient points. First, without war in Europe, the U.S could potentially have stripped, to some degree, her Atlantic fleet and sent it to the Pacific; much in the manner FDR stripped units from the Pacific Fleet to reiforce the Atlantic prior to Pearl Harbor. Second, without war in Europe, the U.S could have sent a far greater number of troops and supplies to the Pacific with the shipping they were using to convoy goods to Britain.
But thirdly, and most importantly, how were the Germans going to threaten us. First, a Navy that can’t reach England isn’t going to reach the U.S, especially with the Royal Navy in their way. Second, the Germans had NO strategic bombing capability capable of reaching the U.S at that time. Third, the Germans were already overextended militarily. The bulk of their Army was in Russia. They had troops fighting in Africa. They had garrisons in France, Belgium, the Netherlands, Denmark, Norway, Greece, Crete, Yugoslvia, Romania, you get the idea. They had neither the troops or air units to cause us any anxiety.
As to the atomic bomb, Germany’s development of nuclear weapons was derailed by-Adolf Hitler. He refused funding for scientific projects that couldn’t deliver the goods within a year or so. And Hitler considered physics a “Jewish” science. So that bomb was coming any time soon.
The U.S had strategic interior lines against its’ two enemies. They could have concentrated their forces, especially air forces, against the Japanese, crushed or left them to starve, and then turned their attention [if necessary] to the Germans. Japan didn’t have to be invaded. By 1944 we had destroyed almost all their fleet, left them with pilots suitable only for target practice, cut them off from food and resources, and could turn the entire country into a cinder.
It's not clear to me what we are disagreeing over.
Did FDR want war against Germany?
Absolutely, that was his primary focus and war with Japan was less important.
FDR's problem was that wily Hitler refused to give him a good-enough reason for going to Congress to ask for a declaration of war.
But the Japanese were less savvy -- or more likely, just more desperate for raw materials.
Squeezing on the Japanese could give FDR the "mistake" he needed for all-out war.
Could Roosevelt have taken some other route entirely, one more dedicated towards finding "compromise" and "peaceful solutions" -- indeed, one far more consistent with the long-term historical behavior of our elected Democrats?
Absolutely, and that is what is so surprising about our socialistic Democrat President Roosevelt -- when it came to matters of war and peace, he acted more like Republican U.S. ("unconditional surrender") Grant than previous (or future) Democrats such as George McClellan, Woodrow Wilson or, oh, pick one: Jimma Carter.
No, on matters of war & peace, FDR was often as Republican as you could expect from any Democrat.
Personally, I attribute that to the influences of his Republican Secretary of War, a New Yorker, Henry Stimsom and, of course, General George Marshall from an old Virginia family.
So maybe these folks helped put some spine into what might otherwise have been your typical squishy Democrat leadership?
But I doubt it.
I think Roosevelt hated Germans as people from his boyhood experiences with them, and his natural sympathies for his fellow countrymen, the Dutch.
And like many others he shared the conviction that Woodrow Wilson's weak policies after the First World War lead directly to the Second.
As President, Roosevelt wanted to see the Germans so thoroughly defeated they would never again threaten anyone militarily.
So nobody had to "put some spine" into FDR.
"Unconditional Surrender" was his stated goal at Casablanca, in early 1943.
Of course, like any Democrat, FDR was eager to kiss the *ss of a Communist dictator like Stalin, but at least in Roosevelt's case, every time he puckered up his lips, hundreds of thousands of Soviets, not Americans, died killing Germans.
So it was a solid working relationship, appreciated by both parties.
So, what exactly do we disagree on?