Question

Why did nation-states replace European empires?

Answer 1

The populace wanted to separate from the ruler ship of ignorant empires , example being the British and India, India strived to gain independence from the British. Or the empires ceased to see the importance/benefits of maintaining offshore colonies due to costs or rebellion, a great example is England who let pretty much all their colonies gain their independence (ex: Canada), but replaced that ruler ship with alliances or a symbiotic relationship.