Uh, Germany did have a colonial empire. They lost it all after losing WWI, giving their colonies up to the various winning powers.
Spain profited immensely from their empire, becoming crazzzzy rich centuries ago. They mismanaged that wealth spectacularly however is why it seemed like they were poor as crap around the time the others in Western Europe started to really get into overseas colonialism. They peaked early, crashed, and around the same time also lost like 80% of their empire to independence movements when Napoleon messed them up
Slavery was profitable for quite awhile, but eventually the economy moved on to more industrial things and yes the South was increasingly left behind as the North became all about factories. The South is not a place renowned for moving on toward new things easily let's just say.also slavery wasn't good for the economy either but that didn't stop anyone.
The point remains that this does not erase what wealth it did generate.
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It's almost like a country very involved in the implosions of Libya and the literal creation of Syria as we know it, telling others that they alone deserve the blame, is a gross and stupid thing.
Also the thing with living in arrogant myopic asshole countries like each of our own, is being self-aware. The US has a very insular echo chamber mindset, it's true. The Brits absolutely do as well. Now, about that self-awareness...