Quite a bit, actually. Granted, I got into back when the Clans were being introduced. Let's see, Comstar had a civil war between the religious factions, there was a huge communication blackout that crippled most of the factions and sent the Inner Sphere back into a pre-Fourth Succession War period (think starter BattleTech, where salvaging is everything and dueling happens more often than large scale offenses) and some dude managed to conquer the Terran Hegemony and started a Republic that managed to get the Clans and Inner Sphere houses to all work together.

The map is crazy with three new territories run by clans, and it looks like the Clans may have finally retaken Terra. So crazy times in the last 20 years since I last really looked at the series.