This is historically untrue. When complex societies civil war, they tend to fall apart. (Wars of unification being an exception.) Their citizens’ living conditions permanently fell, often for generations, until an outside power subsumed them.

This trend looks to be strengthening as time goes on, probably on account of increasing species-wide firepower and mobility. Instead, peaceful (if politically violent) “revolutions” reboot the society from time to time. One could argue the Great Depression was the last such restructuring of the American system.