The Food Wars' was an infamous war in the history of universe.
During the wars the various fast food chains (or possibly other restaurants) around the universe competed and fought each other to destroy each other's businesses. In the end only Monolith Burger survived as the only fast food chain to survive the wars.
It's not known exactly when the wars occured but it had to have occured before the Space Quest X era. The war didn't destroy every restaurant as some non-fast food restaurants were still around; such as Buckazoid Bill's Arcade and Sushi Bar and Universal Hut of Pancakes at that time.