The believers had waited millennia for their God to return to Earth. In time a new interpretation of their sacred text gained favor. It said God would not return until the Earth was cleansed in a great battle. To achieve this end they established their agents in the halls of great power and gained the ears of those in the highest places.
Once the war began, nations were caught up like dried grass in a prairie fire. Nobody escaped the final purification of atomic flame.
The Earth having now been properly prepared, Yog-Soggoth reopened the ancient gate at Har Megiddo.