Another question about lore breaking, how there can be Dunmer when Nerevarine is still fighting? Shouldn't them to be Chimer until they'll sacrifice him and gets the punishment from Azura?
2nd Era, this is way after the events of Red Mountain.
The most likely time period IMO is this:
http://www.imperial-library.info/content/second-era
This fits perfectly for about 1000 years before and during a time when such alliances would be possible. Its after the Akaviri Emperor has been assassinated. Though it says the Empire has dissolved, more likely they will retcon/explain it as having lost control of Tamriel and put in the struggling state described in the magazine.