A very boring and obvious answer is that they're just supposed to be blanks, not really based on anything specifically and instead fill in "templates" for groups.

Western Terrorists and Mercenaries are bank robbers.
Pirates are pirates, probably from Somalia.
Revolutionists don't seem to be anything in specific, just a militarized arm of some communist organization.
Ultranationalists seem to be militarized rednecks.
The Paramilitary and the Rogue Militia could be really anything but I think they're supposed to be eastern European irregulars.
No clue what Arctic or Northern terrorists are supposed to be.
Northern Killers are probably some sort of criminal group.

Originally posted by Reman Luss:

A very boring and obvious answer is that they're just supposed to be blanks, not really based on anything specifically and instead fill in "templates" for groups.

Western Terrorists and Mercenaries are bank robbers.
Pirates are pirates, probably from Somalia.
Revolutionists don't seem to be anything in specific, just a militarized arm of some communist organization.
Ultranationalists seem to be militarized rednecks.
The Paramilitary and the Rogue Militia could be really anything but I think they're supposed to be eastern European irregulars.
No clue what Arctic or Northern terrorists are supposed to be.
Northern Killers are probably some sort of criminal group.

Northern Killers are based on korean mob
Paramilitary looks like various anti serbian militias during breakup of yugoslavia
Northern terrorist are based on russian mafia
Arctic terrorists are based on fictional swedish terrorist group in counter strike source
Rouge millitia like you said could be anything, tbh they look like resistance of some sort

Sorry for late replying. And yeah! You guys got it right.

Just like Reman said, Ultranationalists are based on the militarized rednecks, and the models are inspired by the Russian Ultranationalists from CoD:MW2. ("No Russian" one.)

Paramilitary is a completely fictional faction I made since I've wanted to make an enemy faction against my Military SNPCs at that time. But their models are based on a military clique especially around the eastern european area just like Siegma said.

Northern Killers are based on the Room 39 Agents, and their models are based on the Korean Mob from GTA IV. (The North Korean gangsters.)

Revolutionists are based on the radical communist group like Red Army Faction.

Western Terrorists are based on the Bank Robbers from GTA 5/Kane & Lynch series.

Mercenaries are based on the Professionals from GTA Online.

Anarchists are fictional stereotype chemical terrorists.

For Survivalists(Northern terrorist before), I had no exact concept for them at that time, so I just made them as some kinda "Terrorists from Cold Area" lol
After I've changed their names into Survivalists, They're now basically based on the Survivor groups from some Post-Apocalypse movies.


Some of the groups are based on the Terrorists from Counter Strike series as well.

Arctic terrorists are based on Arctic Avengers, which is a fictional swedish terrorist group.

The Rogue Militia are based on the Midwest Militia from CS:CZ.

Pirates are based on the Pirates from CS:GO.

the middle east ones are based on the ISIS and taliban. one model is even modelled after abu musab al zarqawi