Calvinism, in brief, for those unaware:
Free will isn't real. God makes literally everything happen, and if you complain about it you're complaining about God.
Why does God let bad things happen to good people? Fuck you, that's why. Are you questioning God?
God already decided if you're going to Heaven or Hell, probably before you were born. There's nothing you can do about it. It doesn't matter if you try to be a good person, or if you accept Jesus, or if you go to confession, or if you saved five thousand orphans from a burning building. If God ~mysteriously~ decides "fuck you, burn forever", that's your fate.
However, God likes to show little signs of who he likes. Say, having lots of money, or being hot, or not having horrible illnesses. Good things happen to "the elect", who are people God likes. Bad things happen to everyone else.
Rich people are probably going to Heaven, and they're just better than you, because that's God's secret sign that he likes them more than you. Why? Because fuck you.
If bad things happen to you, it's probably because you deserve it and you're going to Hell. Likewise, if you're poor, ugly, or disabled, you're probably going to Hell.
All of this bullshit has of course had a heavy influence on:
Capitalism, because having money isn't a sign that you're exploiting people, it's a sign that God mysteriously wants you to have nice things. Nothing you can do about it, free will isn't real!
Imperialism, because if you succeed in taking over a place and stealing all their stuff, that's a sign that God likes you. If God liked them, it wouldn't have happened, so you're really following God's plan. And torturing people who are already going to Hell barely even counts, they probably deserve it!
American exceptionalism specifically. Consider the above, and mysteriously, all the native people start dying, leaving vast tracts of land for your people to settle. Well, gosh! God genocided a continent to show that it was secretly always ours! He must really like us!
Witch trials, debtors prisons, insane asylums, &c. They aren't hot or rich, so by definition, they're probably evil and deserve for bad things to happen to them!
... and half of the other shitty things that happen in our society, basically. Calvinism is horrific and it underlies a lot - especially in the US and UK, because the Puritans and Roundheads were mostly Calvinists.
(This was the religious freedom that the Pilgrims were seeking. The freedom to be horrible antisocial creeps.)