https://www.youtube.com/watch?v=EfB9U7j-ZNA
Second 32, what race is the magician who drives the "plane"?
The same according to the Canon after the burning the Horde had concentration camps and hunted civilians in Kalimndor.
So if they were on the land after the burning they were still defending or committing war crimes.
PS: Not counting the plan to Enslave Kaldorei as Undead. (which depends on what moment of the cannon changes what it is)
Depends on what kind of alliance.
If you join a war with the aim of exterminating a people and their entire culture. You are committing a war crime.
If you want to argue that the Horde would never have followed Sylvanas I'll buy it. But BFA is so badly written that Sylvanas literally said "let's exterminate this race completely" and everyone said "Ok good idae".