General:
* Postbellum: (specifically for the period after a war)
* Postconflict: (more general term for after any conflict)
* After the war: (straightforward and simple)
* Post-hostilities: (formal and emphasizes the cessation of fighting)
Specific to a particular war:
* Post-WWII: (for the period after World War II)
* Post-Vietnam: (for the period after the Vietnam War)
* Post-Korean: (for the period after the Korean War)
Other possibilities:
* Reconstruction: (implies rebuilding and restoring after a war)
* Peacetime: (refers to the period of peace following a war)
The best synonym to use will depend on the specific context of your writing.