battle to end all battles

1. A battle that will be of such huge scale and have such a large impact on the world as to end the need for any other military conflicts in the future. The two nations' armies gathered for the battle to end all battles, to decide once and for all who would rule the disputed territory. There was nothing left of the town after that battle to end all battles. I'm sure the soldiers who fought in World War I thought it was the battle to end all battles—not that it would be followed by another such war less than 20 years later.

2. An especially intense, epic, or high-stakes conflict or confrontation. The two veteran politicians will be facing off in the presidential election this fall, and it's truly shaping up to be a battle to end all battles. Girls, we don't want to referee the battle to end all battles every Friday night. You need to come up with a better system for sharing the car. This playoff match-up between two dynasty teams figures to be the battle to end all battles. Too bad it's happening in the first round and not the finals!