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.