Just think about it, they wanted peace after MoP And They Had it, what did the alliance do in the meantime?
Jaina threatens to end the horde and tries to convince Varian to kill the horde leaders at the end of SoO
Greymane assault horde troops unprovoked and loses the sky breaker
Caila Menethil tries to cause mass rebelions and defections within lordaeron and the forsaken to the alliance
They attack and murder innocent goblin miners who are mining for Azerite
They invade gallwix’ pleasure palace and murder Even more goblins and attempt to assasinate gallywix
This was all after ensuing peace with the alliance after Garrosh. The Horde didn't provoke the alliance one more time after that