Question

what led to american individualism?

Answer 1

What makes you think it's uniquely American? I'd say every human being on the planet would like to be left alone to pursue his happiness in the way he sees fit. I don't know a soul who likes to be told what to do by people who events prove are no smarter or nobler than himself.

What may be uniquely American is the expectation that this is possible, while still maintaining public order and being charitable to those less fortunate. That all you need to do is vigorously reject the sweet-sounding lies that ambitious people tell you, that if you only give them your liberty, vote, and money they'll make everything better magically. Reject all attempts to get you to believe you can get something for nothing, i.e. some good for yourself without building it yourself. It's a simple prescription, like the fact that you can lose weight by eating less and exercising more, but it works very well.

Unfortunately, the princes, Dear Leaders, aristocrats, and bureaucrats of the world don't want anybody to hear that message, or pay attention to it, so they work very hard to conceal it, or muddy it up by arguing that your wish to be left alone is essentially equivalent to wanting to abandon other people. Not sure why anybody falls for that, but they do.