>>910383/pol/ wasn't the catalyst, that was the hostile co-opting of western media and anti-consumer corporate practices reaching an intensity that embittered too many anons and too many recreational activities that those anons used as an outlet and discussed extensively on 4chan. Everything /pol/-related that's happened since is some combination of that same reactivity and political extremists taking advantage of a widespread discontent with ideologies that oppose theirs. From there the shitshow has burned higher with opposing ideologues organizing off-site in attempts to raid and subvert boards they think are amenable to either their opposition or to themselves. Now even politically uninvested anons indirectly assign themselves to factions based on cancerous behavior they see perpetrated by /pol/, anti-/pol/ or one falseflagging as the other, post complaining about one of them and invite both of them in to argue for or against them.
I guess the only way to have avoided it all entirely is if 4chan had been kept an entirely otaku-oriented image board.