Death by a thousand cuts
The 21st century world has a stable makeup then. Its constituents, for better or worse, are as they are. Certainly there are some despicable regimes here and there which may fall in the next 20 years or so, though we may be sure their successors will be local, not imposed from outside.
Why is all this happening?
Firstly, invading a country is now more difficult and costly, especially when most people are against it in spite of attempts to distract them with propaganda.
It's our land, and we'll pray, govern, and organize the economy as we see fit.
Also, a century ago, colonial authorities enjoyed a measure of stability, at least until a revolt broke out. But from the early 19th century onwards, occupied nations made use of intermittent crises or the imperial power's weakness to end its occupation for good. That gradually reduced the number of colonial states.
The process has accelerated today so that from the very start, the invaders rarely get a break. They face sabotage, violence and terrorism, however you might interpret those words. The pushback sounds like this: It's our land, and we'll pray, govern, and organize the economy as we see fit. However, while this slogan is good for fighting invaders, it could also easily be weaponized by a home-bred dictator, who'll tell you the exact same thing. Nationalism, then, is crucial to the spread of dictatorships.
Good riddance
Of course, imperialism is more than just marching your armies into another state. There are many ways of pressuring a country to act in one way or another. However, setting up a client regime has become a rarity, and I have a feeling that this tactic of cajoling countries to do your bidding is set to fade even further.
The great powers send their warships to threaten the debtor country. Try it these days and see how that works out.
Consider all the states, like Venezuela, that owe China a lot of money. What will happen if in a few years, the debtor governments refuse to pay or demand a partial cancellation of their debts, arguing there were irregularities in the first place?
A century ago the great powers would send their warships — in what was termed gunboat diplomacy — to threaten and squeeze the debtor country. Try it these days and see how that works out. Many of the world's debts were initially incurred in questionable conditions and with draconian terms, so, frankly, a lot of that money may be as good as gone — and the world is the better for it.