My friend saw it and loved it, and he’s as political as they come. It is deliberately vague about the political motivations behind the titular civil war, as Garland himself stated that the audience can decide that for themselves. Instead, the movie did its homework in realistically portraying the human impact that a civil war has on everyone caught up in it, and just happened to set it in the US to convey it in a way Americans would understand.
As an aside, if a civil war drags on long enough, it usually just devolves into a bunch of warlords and gangs murdering everyone who is not rolling with them. The stated political ideologies of the factions involved often get reduced to window dressing. So in a way the movie being vague about the warring sides’ politics is fitting.
There is nothing “civil” about a civil war, and my friend thinks the movie got that across quite well.