We can discuss Korea .....
Nothing to discuss really. The USA supported by a UN resolution had every legal right to counter the N-Korean invasion. That they later manipulated the UN to get a resolution, allowing them to further attack a sovereign N-Korea, is what caused the demise and irrelevancy of the newly (1945) restructured UN, till today.
And now Americans have no business in Ukraine so sending American fighter jets and American weapons is illegal.....
Due to the security guarantees given by the USA, UK and Russia towards the sovereignty of Ukraine in 1994, the USA and UK have every right to assist with
whatever means Ukraine, upon having been attacked by someone (e.g. Russia). Why NATO as a whole is involved beats me, since Ukraine is no NATO member. The mere anticipation of an Ukraine being controlled/occupied by Russia being a danger towards NATO members, does not constitute a legal basis for direct NATO involvement, NATO themselves have refuted/invalidated Russia from using the exact same argument.
Any country on this planet however has it's own right to object towards a country using military force to attain it's objectives. E.g. via imposing sanctions (but contradicts the WTO charter). Or to supply weapons, humanitarian and financial means to e.g. Ukraine.
That the individual EU member countries chose NATO to handle their own individual response as a central organization, is what has placed them in a very tight spot with Russia. Since NATO coordinates and
directs military involvement directly against Russian forces, it constitutes an indirect deceleration of war by NATO towards Russia. Therefore NATO and Russia are basically at war
with each other already.
If NATO would simply reflect towards e.g. a coordination of weapon supplies requested by Ukraine, everything would be quite in order. If however e.g. a NATO member such as Poland is constantly bringing in demands and proposals publicly - to arm and train Ukraine with whatever - NATO again gets directly involved towards Russian forces. The same goes for intelligence related info supplied via NATO to the Ukrainian MoD, as a result aiding directly in killing Russian troops.
Due to these factual circumstances, countries such as e.g. Iran, China or India or whoever, have also the right to assist, support e.g. Russia by whatever means.
The USA did exactly that during the Iraq-Iran war. Therefore the USA was clearly an active war participator against Iran, independent of not having had boots on the ground.
The same goes for all these Israel-Arab wars - both the Soviet-union and the USA having been direct participants.
It could have been so simple - UK and US boots on the ground and Putin's agenda would have ended latest by the end of last year. But these two had to get the whole world involved.
Well global politics instituted and directed by a huge bunch of incompetent politicians - what else should one expect?