The Blood was never the cause if you payed attention.
It was Kil'jaeden who sent visions of past shaman and loved ones to not just Ner'zul but all Shaman that convinced the Orcs the Draenei were the enemy.
Warlock magic also had an effect on the Orcs as well. They started to forget to forget their humanity leaving their wounded to die on battlefields even though they could have been saved with just first aid.
In WoD the elements also witness the vision from the shard of the hourglass its not just Grom. The horrors that would happen to Draenor convinced the elements to push the Orcs to war which is why the Iron Horde retain control of the elements.