Power corrupts and the US has deluded itself to think everything it does is justified, even when they are breaking their own laws to fund contras in the Americas
So, at the outset, you do concede they have the power, right?
Or more appropriately, they have the capability and ability to use their resources to project and wield power to promote their own interests?
How is it any different from
Safavid Empire, as an example?
using chemical weapons in huge quantities in Vietnam
Defoliants. Just like any herbicide used in gardens today? Can you provide citation of any nerve/blistering agents that were used? Because, even your normal mortar HE round can be considered a Chemical Weapon.
or massacring hundreds of thousands of citizens with WMDs in Japan, etc (the list of US crimes against humanity is virtually endless).
A figure of 129 to 226 Thousand KIAs is listed for the casualties from the two instances of use of Nuclear Weapons in Japan.
The Bombing of Dresden between 13 to 15 February can be argued to be an instance where, had the bombing not been interspersed over the three days, could have led to an almost similar casualty figure. It still was estimated to be 25000, although actual figures can not be commented upon due to churn in population at the time.
Military invasions are usually by nature illegal unless in self defence (although self-defence wars are not usually called 'invasions') or authorised by the UNSC.
Invasions are always illegal if one is to go with your rationale. Even self defence shall, technically, limit you to merely opposing the forces that enter your territory, with no justification of crossing over into other's territory.
For the former, you could argue Israel's invasion into Egypt in 1973 qualifies as an 'invasion' in self-defence.
But 'illegal' nevertheless, no? Because your rationale remains of US & illegal based on premise that pursuance of national interest is illegal. If you extend the argument to 'at the cost of others', then a so called self defence invasion is also illegal.
For the latter, NATO's use of force in Libya was legal in that it was authorised by UNSCR 1973 (although the latter stages of NATO's operations in Libya clearly went beyond this legal mandate).
So now it becomes legal? Similarly, what are you views on use of force against Iran then? The statements coming out from Iran, at times, does give legitimacy of 'self defence' invasion by Israel, if your logic is followed.