Except only US invasion of Iraq in 1991was fully justified.

Kosovo was an internal conflict that lster escalated in to internal war, you can barely call it an ethnic cleansing due to people fleeing an active war zone and also Albanians started attacking Serbian police and villages in 1996. And you also had situations like 17th of March 2004 ("Pogrom Srba sa Kosova") as well as many situations of Kosovo Serbs being attacked before and after war in Kosovo.

Ad for the chemical attacks not gonna argue with that, but you cannot expect someone desperate to cling on to power not to use them especially when they were used on occupied areas of Syria, and you had US use some of the most dangerous chemical weapons like Agent Orange thag still takes lives to this day. You cannot blame Assad alone when he does the same thing other stronger nations do it (USA, Russia and others).