2nd Era, denoted as 2E or CE.
A Dragon Break is a bend in time so severe that an alternate universe is created for unknown reasons. The Dwemer's Dissapearance created a Dragon Break, and so did most of the game endings, most notably Daggerfall (where it manifestefd as an explosion suddenly solving everuy political problem) and Oblivion, where Akatosh himself had to clean things up.
I think TESO's backstory will clear up where time may have diverged. I'm thinking Red Mountain.
Oblivions ending is not a dragonbreak.
It was the manifestation of the avatar of Akatosh, who released from the Alessian pact banished Mehrunes Dagon as the final and closing act of his alliance with the Septims.
Only a few have happened that we know of.
There is
the dragonbreak or the middle dawn when quite possibly Akatosh as we know him today was created.
There is the apotheosis of the Triune, where they rewrote time in order to always have been the Dunmer patron deities.
There is the ending of Daggerfall or the Warp in the West that reconciled all Daggerfall's endings by having them all happened at once.
These are the only ones I can think of.