>That wasn't in XX century however. They were universally gone by mid-century.
Mostly because of those pesky Bolsheviks being a new worry of the colonial powers, standing in as an idea that their rule can end, and socialism inspiring all kinds of anti-colonial national revolutions (from Vietnam to China, and from Africa to Latin America). So, there's that.
Besides, neo-colonialism still dominates the developing world. It's the bigger fish like India, Japan, China, Brazil and a few others like Indonesia, that got away from it and managed (more or less successfully) to take their fate into their own hands instead of being played and meddled.
And yet, a few western powers had enslaved and controlled 2/3rd of the world.