Military action
A war between the Veskarium and the united Pact Worlds
The Veskarium invades the Golarion system, making first landfall on Triaxus in what would be called the "Battle of Aledra" and ravaging the mountaintop city of Aledra. Though a multiworld alliance manages to drive off the invaders, the ensuing "Silent War" with the Veskarium costs innumerable lives and prompts the formation of the Absalom Pact.
During the pseudo-war, the two systems remained each other's greatest threat: skirmishing over planets outside the direct authority of either autonomy, or else engaging in limited space battles along the cordons between their systems, too evenly matched for either to commit to a full-scale assault.
After more than 200 years of conflict, the "Silent War" between the Pact Worlds and the Veskarium is interrupted when The Swarm invades both systems.
In order to survive, the two governments agree to end their hostilities, working together to successfully rebuff The Swarm's mindless destruction.