I've heard multiple times about a bit of lore that holds that 4chan once tried to brigade Stormfront, causing Stormfront to brigade back, and that was how the cross pollination occurred and started turning 4chan fascist.
No idea if this is true but it sounds plausible.
I think the much more likely explanation is that 4chan always existed as a genuine counterculture (which was particularly true in the age prior to the late 2010s, when the internet was like a completely different world to real life), and reflected the rejection and inversion of certain societal mores. The rise of a far right current in 4chan exactly mirrored the kind of progressive fundamentalism that emerged in the dominant culture from around 2013. The outer zeitgeist started to abandon a 30-50-year term of post-racial thought, and immutable characteristics like race and gender started to become meaningful as tangible social capital in a kind of "official" way, as ideas like the progressive stack filtered from online circles and Occupy Wall St, through academia, into the halls of power and governments. The emerging racial consciousness of places like 4chan were a direct (and predictable) reaction to that.
The reason that places like 4chan became a far-right haven and other areas of the internet didn't has nothing to do with whether people tried to raid Stormfront in the 2000s, but is purely a matter of the firm-handedness (or lack thereof) of their respective moderation. Prior to the 2010s, many less-moderated areas of the internet had a variety of political persuasions, but from 2015 to the present day, there is a very strong correlation between the prevailing political leaning of a space and that space's ideological moderation strength.
In its earliest years /b/ started prank calling the radio show of nazi Hal Turner, then messed with Stomfront as the conflict widened. There was little activist component to this. They just thought it was funny to rile up people who took themselves very seriously.
I don't think there was any real reverse colonisation. 4chan's userbase was always whimsically racist and A Wyatt Mann cartoons were everywhere long before the conflict. moot and WT Snacks implemented some interesting word filters that I can't repeat here without my post getting hidden. Everyone was hateful, but not full of hate.
I think very little has changed in twenty years really. Feral male behaviour is just arbitrarily right-coded now, when it wasn't during the Bush era. Most of the kids screaming bix nood probably voted Obama in 08. Politics is window dressing on timeless brand of petulant contrarianism.
If you're a parent, teacher, or intelligence officer worried about a "crisis of radicalisation", the worst thing you can do is take this stuff seriously. Just call your son gay until he grows out of it.
The edgelord thing goes back way further than 4chan and Something Awful. I remember plenty of racist fascist rapist satanic misanthropist kitten smasher edgelords from the BBS days. It was not serious, though sometimes it was I hate my dad and I just got the new NiN album serious.
At some point something did change though. It was around the same time as Gamergate and it’s been written about extensively. I’ve been into edgy hacker adjacent culture since like 1992 and when the “actual not ironic” stuff landed it was immediately recognizable as something unfamiliar and different. I’m still not sure how many people got “pilled” versus how much of it was some kind of weird collision with normie spaces where people didn’t get the culture.
There was a generational shift in there too. OG hacker culture was GenX and older millennials, the people who grew up with the net pre enshittification. The /pol stuff and GG seems like younger millennials and GenZ.
I am not pretending to have a clue and I don’t think anyone truly does. It’s all a very complex soup of memes and people and influences.