Taking a stab at it: Someone associated with Varga (Or possibly Varga himself) is trying to wipe out Stussies due to a (relatively) old familial grudge.

In my mind, this justifies the existence of episode 3. SPOILER

I also tentatively suggest that there's some themes about the importance of heritage throughout the season, which could culminate in a reveal of this nature. This is most evident in Yuri, especially when Paul speaks with him, but I think the Stussy brothers also incorporate some of this theme into their relationship.

Bonus guess: This old grudge against the Stussies originate in the first story in "A History of True Crime in the Midwest", which takes place in the 19th century.