You're going to get a LOT of reductive and low effort answers from Lemmy radicals. But this is a super complex question, and there's not a 5-second ELI5 answer if you really want to understand.
Also, when the radicals scream at you, there's going to be a core of truth. They're going to yell about colonization and empires. That's a major factor, but not an exclusive one. However, for getting radical and rabidly furious its all they'll bother posting to you.
Things to investigate, because answering this for yourself in a meaningful way is going to take a while and require study. Here are some topics but NOT an exhaustive list:
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Colonization
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Resources (natural and otherwise)
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Schooling, education, etc.
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Stability, politically and otherwise (note this will have overlap with colonial and non-colonial powers destabilizing things intentionally for geopolitical gain)
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Infrastructure (transportation, economic, water, medical, etc.)
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Medicine as regionally practiced, traditional vs based on the the scientific method.
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Geopolitics (isolationism, etc)
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Geography (i.e. the US's greatest asset is its location, it neighbors no enemies and its main enemies are separated by an ocean. One of the key reasons the US focuses on the ability to project force)
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Religion
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Corruption (politically and non politically)
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Crime and non-military/nation based violence (also could get grouped under personal safety and security)
And again, honestly, a lot of these topics will overlap, but that's what I mean by there isn't a quick, easy answer.
And the reductive stupid answer is just yelling colonialism.
There's a reason people get PhDs in this subject. It's not a quick, easy question.