When the US was founded it excluded about 94% of the people from within its borders from participating. Slavery existed on a mass scale throughout the world’s early, liberal (so-called) democracies, or often their economy was subsidized by slave labor abroad in their colonies.

Yup. And by today's definition, I don't think that's a democracy.

The idea that industrialization or “democracy” (not even sure how you are defining it, really) came into existence suddenly isn’t accurate

I'd define it as one end of a continuum of incentives for leadership. In a modern democracy, pissing off the voting public is a guaranteed lose condition. In North Korea all that matters is keeping the the people just below you loyal and the people just above you happy (yes, I see your domain, no, I don't want to hear your conspiracy theories right now, I'm having another conversation). Kim Jong Un doesn't need to care if his people are starving as long as his generals keep their soldiers in check for him, who will in turn keep the civilians in check. Maybe he does, I think some dictators do, but he doesn't have to.

Agreed, it didn't happen suddenly at all. It took centuries of both reform and revolution and counter-revolution. But, it did happen unexpectedly after a lot of the same, and I fear it going away again if I don't know why it's here.

Also, I'm not sure if industrialisation is connected to the growth of ideologies, although I suspect it based on timing and certain shared ideas.

But weapons themselves aren’t necessarily going to singularly shape the way in which social conflict resolves. Military technology is important to these developments, but ultimately a part of the larger social system that is always changing to either maintain itself or undergoing revolutionary change.

Agreed. That's the only variable I can find from the last 2 centuries that didn't exist anywhere in the preceding 50 centuries or so, though, at least to date. My next best guess is that the awareness of progress itself fueled it.