The Avengers, Vol. 1 #169 (1977)

If We Should Fail--The World Dies Tonight
Three Avengers are at home on one of their slow evenings when they are attacked by a man in armour. They subdue him, only to learn that his goal is to die in combat, triggering a chain reaction that will destroy the world. The Avengers must find a way to put the pieces together and save the world before it's too late.
Release Date: 1977