And I'm gonna have to disagree. The US had one of the most vibrant, fasted growing, and radical socialist movements. It was steadily gaining support, even among native born Americans, all the way through WWI, and was only decisively broken by the Red Scare, the mass deportation of radicals, and the tightening of voting and citizenship requirements that broke the left, and ultimately led to its long term co-opting.
This only occurred because of very well thought up publicity campaigns, highly extensive systems of propaganda that were almost unheard of in the rest of the world until the rise of fascism, and of course more than a healthy amount of violence.
If there was any country that had the most raw disposition for socialism, it was the US. Which is, paradoxically, why it didn't happen. Because it was all too obvious what a threat it was to the highly class conscious American political establishment. They knew, a whole lot better than their European counterparts, that it was necessary to establish the legitimacy of the current system in a fundamentally new way. Whereas, in Europe, the long legacy of the ancien regime meant they relied upon the failing old traditions of Church and traditional authority to keep people from joining unions, or from voting for socialist candidates.
In America, you had a population of people, many of whom were radicals fleeing oppression in Europe, whether for ethnic or religious reasons. You have a native population that is deeply suspicious of the growing industrial establishment, and is strongly egalitarian in its ethos. They believe in living by the sweat of their brow, and they resent what they see as the parasitical nature of big business.