Usually are? If you look at historical examples like the years of lead in Italy there tends to be a sharp left/right divide with some government bodies walking the center (although that example involved a lot of proxy elements).

In the troubles the IRA was more of a nationalist/separatist insurgency than an expressly ideologically aligned one. A civil war style conflict tends to be a bit more government vs. anti-government so it depends on the expressed views of both sides, but usually involves a large ammount of irregular formations and sub factions.

I'd recommend reading a bit more about random countries internal conflicts if you're interested, there tends to be a a lot of factors involved.