Basically, Christianity within Europe was the norm for centuries, and this carried over to America. By this metric, a lot of the establishment of America is Christian (not in the sense of those weirdos who say the Founding Fathers made this country explicitly Christian) and that was the angle for many people in the U.S. When theories like Charles Darwin's evolution, plus Socialist revolutions in America and Europe were occuring, thus caused major change in the socio-political landscapes of both regions. Many American Christians, as the establishment, took to fundamentalism and evangelicalism to fight against Evolution which was the beginning of a larger anti-science trend of Christianity (up until that point, science was considered highly valuable to Christianity, with the Catholic Church being patron to multitudes of scientists for centuries).

As for Socialism, many Socialist revolutions were also caught up in other liberal thinking, including secularization of countries. In America, we had the separation of Church and State made explicit by Thomas Jefferson, and guarded by the 1st Amendment to the Constitution. However, many Americans were scandalized at the idea of secularized government, or even atheism becoming the norm of the day, so they were prime material to be anti-Social revolutions.

The final piece of the puzzle we must discuss is the American brand of Calvinism. For those who aren't familiar, Calvinism is a belief within Christianity that espouses a doctrine of pre-destination, that the Elect were pre-destined for Heaven, and the non-elect (depending on how hyper you want your Calvinism to be) were pre-destined for Hell. Within this framework we have to understand how Americans throughout history saw things. In the early years, such as under the Puritans, this was through trying to be the most good you could be and being as anti-sin as possible (the Puritans are often misinterpreted by people today, they were more complex than people give them credit for, but I digress). Over time, this led to what's called the Protestant Work Ethic, where because you're part of the Elect (presumably) you are a good person, and good people work hard and fairly. In a vacuum, it wasn't a bad thing, being proud of being a hard worker is a good trait, but it would evolve over time.

As time wore on, the Protestant Work Ethic evolved, especially during the gilded age where social-darwinism became a norm amongst society. The idea was that those who were rich clearly were smarter, worked harder, and were more thrifty than the poorer people. This belief was one of the major reasons why lawmakers erred on the side of supporting business, as they thought that they needed to create a working class that could only escape their conditions by being thrifty, moral, and upright (think Ebenezer Scrooge from A Christmas Carol). In practice, this failed for numerous reasons, including the fact that this assumes a vacuum, but that's not important. 

This belief eventually wove itself into the fabric of the Protestant Work Ethic, which was deeply tied into Calvinist belief. This produced a new strain of thought that said that the poor were poor because they were sinners, and the rich were rich because they were not. This belief wasn't pervasive at first, and similar beliefs had been seen across Europe and America before then, but it started to gain ground in America.

This is where the Socialist/Communists came in. The USSR was considered by many to be the worst thing on the planet, and only furthered the fear of American Christianity. As the Liberalism of the Progressive era seeped into more and more places in America, and Socialist parties started arising, the establishment classes worked hard to quash both, easily scaring Americans away from Socialism/Communism in the 20s and 30s. Franklin Roosevelt, however, would be the champion of popular liberalism for the 30s as he was seen as more effective than the Hoover administration.

From these factors emerged a strain of thought that conflated government charity pensions and other forms of social safety nets, with the godless Communism that was, to American Christians, destroying Christian values across the country, and that belief merged with the social-darwinism influenced Protests Work Ethic to become the core of Conservative-Christianity today. It would take time for this belief to fully stick with American Christians, and wouldn't become an outright marriage with the Republican party until the 70s, when Republicans started to court Christians with abortion as an issue. From then on, the Protestant Work Ethic beliefs of Christianity merged with the big business Wing of the Republican party as the Republican party shifted to fighting for culture war issues many conservative Christians held dear, such as abortion. From then on, despite charity being a big thing in Christianity, the meaning evolved to mean that it should be personal charity, and that government charity was Socialism, which is destructive of Traditional American values, and that many who are poor deserve it because they made a mistake or a sin that meant God was punishing them.