History is more than a century long, but a modern state by military standards has been a thing since around the time of the civil war when rifles replaced muskets and industrialization became a thing. That's the point where unlike in the Napoleonic era, you can't win decisive victory on the battlefield, things depend on political will, manpower and economic function.
Using your example of the British Empire, India didn't win independence through combat, civil disobedience made it politically untenable for the British to continue. That had far-ranging effects on what was left of the colonies.
One of the arguments core to an advocate of the 2nd amendment with respect to this issue is that a citizen militia, equipped with small arms, would be capable of deterring a government from taking some action. It's an increasingly absurd position.
I think you have an absurd understanding of history if you believe all of this decolonisation happened nonviolently. Almost every independence movement relied on the threat of violence. You are using the civil war itself as the starting point, a brutally violent regime change. Ireland gained its independence from Britain in no insignificant way thanks to violent means. Most African nations gained their independence through violence. And even India was not just freed through a barefoot bespectacled man walking around singing kumbaya. Simplifying it to mere acts of civil disobedience is grossly misrepresenting how complex the situation was.
What a contorted argument. I assume that the British empire wasn’t a modern state, and that history is less than one century long (and full of holes).