It starts in the Base Game.
Pact zones, the Reachmen attack the Rift with the "aid" of the Worm Cult. Covenant zones, the Reachmen attack Bangkorai. Then Wrothgar, the Reachmen are invading Orsimer lands. DLC Dungeons, the Reachmen use an old Blood Forge in cooperation with Minotaurs to raise an army and take Falkreath Hold, and now in Harrowstorm they, under another "Patron" are getting set on attacking Haafingar Hold.
Throughout the game the Reachmen have been on a path of aggressive expansion, always getting halted by the efforts of the Vestige of course, but other efforts keep starting, and get bolder. Will this culminate with Greymoor? Eventually the Q4 Adventure Zone hinted to be Markarth and The Reach? Or are they just pawns once again of another badder foe. (obviously the latter) Still, it's interesting how far reaching this has been.
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