I think the common feature of Germany and Japan is that they saw it reasonable to pursue aggressive foreign policy, including war, to pursue goals they believed would provide stronger long term economics for their countries, including better resource access and space for their people beyond existing borders.
They both saw opportunity, although in Japan's case it rightly identified it's ability to take over from Britain as the key naval power in the East...and wrongly identified whether it would be able to avoid conflict with the US.
As time went on, and it became somewhat obvious that a general war would need to include fighting the Americans, Japan tried to land a heavy blow, so they'd have time to secure that they needed, have a strongly defensible position, and then negotiate from a position of relative strength. They were encouraged in this by a German High Command who'd tried to avoid confrontation with the US, but now realised that whether it was official or not, US economic power was having a major impact on the war. Better for them if the focus for America turned from supporting the Allies to direct conflict with Japan.
I think they may have misread U.S. public opinion to some extent, considering us to be isolationist, divided, and weak. They didn't think Americans would have the stomach for war, and they probably couldn't understand why we would have any interest in what they were doing anyway.
I think there may have been the notion in Germany and Japan: "Why do they even care? Britain has their empire, why can't we have ours?" They saw themselves as "have nots" while the British and Americans were viewed as fat cats who have everything. Hitler's peace offer to Britain was to offer to leave their Empire alone as long as they allowed Germany to get what they wanted (mainly economic control over Eastern Europe). Most would argue that Hitler was too treacherous to put any faith in any agreement he made, so his offers for peace were refused. Same with Japan. Neither could be trusted.
But the big punch didn't do enough damage, the Japanese (like the Germans) overestimated their ability to strengthen their economy during an active war by strategic conquests, and they had no wiggle room when they lost (or even drew) key battles.
The irony is that the U.S. was still largely against the idea of entering the war - at least until the Japanese attack. The big punch had the opposite effect that the Japanese were hoping for. They thought their attack would send Americans into a panic of fear, where we'd be so afraid and awe-struck by Japanese power that they would cower and run away from the fight. Hitler seemed to have the same viewpoint, seeing us as some weakened nation of "mongrels."
(A similar mentality can be discerned even among the 9/11 bombers, who ostensibly thought that if they could show Americans how tough they were and how much damage they could do, Americans would just fold up and wilt and demand that our government give in to terrorist demands. The idea that some "big punch" or bloody nose is enough of a blow to compel American compliance has been pervasive among many of our enemies, but it's really quite foolish.)
You're right, though. The very nature of war changed through this period, and it's almost unthinkable now to have a series of major players simultaneously pursuing aggressive programs of forceful acquisition. Wars are generally fought over other matters.
Indeed, Ukraine is somewhat of a throwback, and clearly a number of countries have taken the approach of providing direct material and economic support...but not boots on the ground.
Since the end of the Cold War, a lot of wars have been civil wars to one degree or another. Most nations don't really fight each other anymore, but some governments still make war on their own people (or vice versa). However, there are also old enmities and bad blood from past wars which can still cause flareups on occasion. Some people are willing to let bygones be bygones, such as between the US and Canada. We had our hostilities in the past, but nowadays, we're all pals; no one is going to get into any fights about it.
Germany seems to be on good terms with their former adversaries, and Japan also appears to be capable of acting as a responsible and mature regional power. There doesn't seem to be any threat of any great resurgence of nationalism in either of those countries (although I could be wrong).
But Russia and China appear to be more nationalistic, and even some countries of Europe seem to be inching in that direction. Africa and the Middle East also appear to be driven by nationalism, at least as much as religion may drive them. In Latin America, they appear to be driven more by politics and economics, although their wars have been relatively mild compared to the wars of the Eastern Hemisphere. From a U.S. standpoint, Latin America is our "soft underbelly," and if an outside power wants to get at the U.S., their best bet would be to try to woo and romance one of our Latin American neighbors to the south. Nicaragua, Cuba, Venezuela, and even tiny Grenada have sent U.S. leaders into conniptions.
I agree that the war in Ukraine is a throwback, although it seems rooted in old enmities and bad blood from previous wars.