When they were young, the alpha children learned about pack wars from the werewolf history books and also from their pack elders. Back when the werewolves first came to be, there were a lot of small packs that fought for territories. Over time, the smaller packs merged into bigger packs, usually through pack marriages. Fights over territories decreased as the number of packs decreased and vacant territories were claimed one by one.
Although werewolf society evolved along with human civilization, they were still bloodthirsty beasts. When conflicts between packs arose, they quickly resorted to violence first and then peaceful discussion. Over time, peaceful discussions were encouraged and violence was repressed. When peaceful discussions no longer helped, then wars were necessary to offset the accumulated malice.
The last war that was fought was the one between the Silent Walkers Pack and the Night Prowler Pack.