Era beginning/end
The first age began with the defeat of Bellerophon. The first age was a time with millions of gods and immortals roaming and rampaging on the planet. Very few nations came and stayed in this era, and the great god war would come right after.
The Great God War would end with the death of Babel. There were millions of gods and immortals, but after the war there were only a few thousand left. The only gods left were those that survived, fled or were triumphed in the war.
The Second Age would be the longest and it would see the birth of many nations at the hands of mortals.