I'd argue a lot of people have asked the Americans to be involved. Nearly everyone has.... usually one side is saying they don't want help. It reminds me of this: https://www.youtube.com/watch?v=4zYb9UW4oH8
There were a few bad wars, but most were good, and more often then not, the most valid criticism is not that the US got involved but that they got involved too late. The Americans always do the right thing after trying everything else. WW2, Bosnia, Iraq (unpopular but the guy was a mass murderer, you can't defend not removing him unless you acknowledge that the middle east needs brutal dictatorships), and so on. The US has definitely been a force for good. There might be one united North Korean regime if not for the US.
Vietnam the most lambasted war of the 20th century was not just an ideological war, it was an affront against communism that up until that point had killed tens of millions, and if the American public had the wherewithal to understand that then the US would have won. Hell, they won in Vietnam in every way imaginable. The fact that the Tet offensive was seen as a disaster in the US despite being the worst blunder in modern military history by the Vietcong is insane to me. An absolute joke that, along with not providing deterrence when they broke the CF agreement, led to many more deaths by communism.
Pax Americana has lead to a relatively stable world despite the fact we are at the height of weapons technology. The fact that the most brutal wars these days do not have the same scale of major genocides and weapons of mass destruction that plagued the 20th century is because there is a monopoly on the military by one country. Frankly, everyone is afraid of the US intervening, or was, before Obama. Obama intervened in weird ways in places like Libya that did not need intervening in and drew red lines in Syria then let people walk across them. If you put a line in the sand and you're the biggest, baddest cat in the alley, then you damn well better not let anyone cross it. Trump proved in one attack that if Obama had been decisive, the Russians would have done nothing. There are other dominoes that were affected by Obama's line including the annexation of Crimea.
I think I mentioned I'm not even American. I just think you guys need to realise what the Roman's forgot in the years before they collapsed... your system is worthy of praise and it is a force for good, I personally think it is the best system. To date. You should have pride in it because it is keeping the rest of us safe.