It has been said that Trump just started WWIII to which I reply, consider the reality. How many casualties and how much distruction has been suffered by the opposing sides? The leaders of Iran may yet try to cause Israel & US harm but considering how one sided it has been so far, they are not likely to have any success.
Besides, I think most will agree with me, if Hitler had been stopped a couple of years earlier, there would not have been a WWII. Consider the lives that would have saved.
Even if Japan had still attacked Pearl Harbor, the US could have turned all our attention away from Germany to Tojo. The Japanese would have fallen much faster. That too would have saved lives.
That being said, I suspect Japan would have likely reconsidered. Moreover, we likely wouldn’t have had a reason to build or deliver the A-bombs. beyond that, most of our speculations would lack any accuracy.