Re: Is there any proof?
To be more accurate....
"- USA attacked Irak twice, still no evidence of mass killings."
USA attacking Iraq was never about mass killings.Iraq 1 was in defence of Kuwait, whom Iraq had invaded. Perfectly legitimate, and not much different to what US and EU are doing with Ukraine at the moment (In Iraq 1 of course there were western troops on the ground, not only material / logistical / political support).
Iraq 2 (incidentally, today marks the 20th anniversary of it) was about supposed WMDs, weapons which UN inspectors had been looking for since Iraq 1 and found nada still in place. US and UK said they had proof but never showed it (and later it turned out their proof was made-up crap). Completely destabilized the whole region for decades, millions killed, lots of political points for the chickenhawk Republicans and billions of arms orders for the military-industrial complex. WMDs found: 0
"USA attacked Serbia - no evidence of war crimes"
There's plenty of evidence of small-scale* war crimes happening in the post-Yugoslavia civil wars. There's also tons of evidence of war crimes happening in small and large-scale conflicts all over Africa, the Middle East and SE Asia, where the rest of the world doesn't fly in shooting missiles now and asking questions later.
"It seems America no longer needs to provide evidence for their claims"
Never have, never will, ever since the days of the Monroe doctrine (aka all the Americas are belong to US)
* of course I don't want to trivialise this, war crimes are always serious, they don't always justify external military intervention by Team America World Police