Ever since both World Wars, there has been a change in general attitudes towards the military and war. There was less glorification and romanticisation of war, especially since WW1 after being exposed the sheer destructive power of the technology of the 20th Century, and less romanticism towards the attitude of might, perseverance, and the will to take up arms if necessary such as although Nazi Germany glorified war and military might, the people around them were not as keen especially when they were informed about the Hitler Youth (especially their efforts to fight in the later stages of the war), and even Hitler's attempts to do a political coup in his early years.
Then, after WW2, and especially in the mid of the Cold War, the attitude towards warfare has started to change - the United Nations was formed with the attempt to omit the change of another world war and the formation of authoritarian rule, and there were the anti-war movements of the 60s and 70s, especially after being informed of the horrifying images and information that were done by the Americans during the Vietnam War.
As a result, the glorification of war and even nationalistic attitudes started to change in Europe but in America, it is a bit different.
The attitude towards patriotism, the romanticism of the collective might of the people during the American Revolution, and the attitude of the world's defender - these attitudes in America persisted even though America was involved in both World Wars and also was the main contender of the Cold War.
So how come, even though Europe and America are allies and even though they both had an influence on both World Wars and even the Cold War, how come their general cultural attitudes towards warfare started to differ as time progressed in the 20th Century?
This is an excellent question for which there is no one set of conclusions. I hope the following is helpful despite the tentative state of the field.
I think the timeline you lay out mistakenly draws a linear trajectory from WWII to today and also conflates attitudes toward war and toward the military. Untangling these two points of confusion can give your some answers I think.
Regarding war / warfare, it is important to note that Americans have not been invaded since 1812, a war which is basically ignored in American education and cultural memory. Attitudes toward war are thus rooted in notions of a deployed force contributing to global order rather than a domestic confrontation where blood is spilled in the streets. So in answer to your question about attitudes to war / warfare, it is natural that American views would be quite different than European views and I can’t think of any time in American history that the views were the same as Europeans’ - the lived realities are just too different to compare.
Notably, attitudes to war change between war and peace time. The best source on this is Adam Berinsky’s In Time of War (2009) which demonstrates that Americans took their cue from political leaders rather than came to rational conclusions about wars. Basically, Berinsky provides evidence that voters view support for war through the same partisan lens as other issues, although I’m not sure if this logic holds in other countries. So in terms of why Americans feel as they do about the wars they fight, that’s simply because they respond to the partisan logics that bring about the wars in the first place.
Regarding attitudes to the military, polling data, most famously from Gallup, demonstrates steady growth in confidence in the US military in the late 1970s (beginning of survey and low point in military public relations) to today, from a low point of 58% (great deal / a lot of confidence) to 72% in 2020. Pew research suggests that confidence in the military is quite high in Western Europe too.
Why in Western Europe and the US is confidence high?
Post-Vietnam, militaries made a big structural change by relying more on professional volunteers than conscripts - many countries did away with conscription completely. This has given the foundation for confidence in an organization people admire from afar and which is populated by those who willingly serve. Administratively, NATO militaries have evolved enormously sophisticated internal policies and warfighting competencies that are quite impressive and are by a long shot the best in the world - thus confidence is well earned.
However, you correctly note that there’s a huge difference in attitudes beyond simply confidence that separates the US from the rest of NATO / Western Europe and indeed from Canada as well. Following the German theorist Alfred Vagts, we can describe this as “militarism” - the celebration of military bells and whistles - which occurs alongside “the military way” (ie just the professional stuff militaries do). So, we can say that since Vietnam Western militaries have reformed themselves and earned respect for the military way in most countries BUT only in the US do we see very high rates of militarism (as per Vagts).
The reason for the rise of American militarism in this technical sense remains a debated question but surely has to do with the following:
the clever public relations efforts of civilian firms hired by the DOD to sell the military for recruiting purposes since the 1980s.
the organizational changes at all levels of military life that DOD leaders have enacted precisely to improve relations with the executive, legislature, judiciary, local base communities, industry at all levels, and critically the media at all levels.
the connections between the high tech industry, the military and the culture industries that intentionally and not have led to a consistent stream of militaristic popular content for all age groups for decades.
the feedback loop of political elites courting the military in an acknowledgment of the success of points 1-3, thereby generating the Berinsky effect noted above. At worst, this has led to a political shield dynamic where politicians pretend they have military support for things that they actually don’t.
This last twist is only possible because of the fifth and strangest piece of the puzzle:
The United States heads a fantastically capable military alliance built on highly professional forces with cutting edge and very “cool” technologies. Thus, we are confident in their ability. Further, the cool factor (in large part a culture industry effect) is reinforced directly by media campaigns to recruit volunteers, indirectly by admiring journalists who write stories in the DOD’s interest more often than not, and by elites at many different levels who try to align themselves with an organization that bends over backwards to make their relations work. Meanwhile, the leadership keeps reinventing in the things that have given it political success and very carefully avoid any suggestion that they are anything but an apolitical, subordinate and deferential wing of the government and servant to the constitution.