Religion, according to Karl Marx, was the opiate of the people. Although not a Christian himself, he lived in a Europe where the Christian doctrine of a better life after death for those who accepted Christ had been used by governments of all stripes to keep the populace docile and accepting of their earthly fate for nearly two thousand years. Christ taught other things regarding the temporal life, but many of these teachings, such as those dealing with turning the other cheek and doing unto others what you hoped they'd do unto you, also tended to help rulers maintain their rule. Ironically, while Marx excoriated religion, many of his own prescriptions were not so far removed from those of Christ.
Religious institutions tend to foster conservatism, if by conservatism we mean resistance to change and the preservation of the existing order. After all, if you believe in eternal truths, handed straight down from God through one messenger or other, why would you want to see any modification of those truths, as interpreted by your tribe, sect or nation.
In modern times we have come to use the terms liberal, or sometimes lately, progressive, for people who welcome change or actively seek it out. They tend to be artists, intellectuals, feminists, immigrants and other disreputable types. In Europe there is an exception to this usage in that liberal is often a term referring to laissez-faire economics, an approach which leads, not so much to change, but to a reinforcing of the existing order.
The USA has developed a political system built around a two-party system, aligned around class, race and religion, but typically holding to the division between liberals and conservatives, with the Republicans most often representing the conservatives and the Democrats usually representing the liberals. Race was the anomaly in this equation, since it was Lincoln's fledgling Republican Party, described by Doris Kearns Goodwin in her book Team of Rivals as “that curious amalgamation of former Whigs, anti-slavery Democrats, nativists, foreigners, radicals and conservatives”, which favored the abolition of slavery. For a century after that, southern whites remained solidly in the Democratic column until LBJ upset the apple cart by passing civil rights legislation, which together with Richard Nixon's southern strategy, assured a solid Republican majority in the ex-slave states for years to come, as well as assuring an even more lop-sided adherence by people of color throughout the country to the Democratic Party.
Conservative groups like to proclaim that America is a Christian nation, or when they're looking for Jewish campaign contributors, that it is based on Judeo-Christian values. Liberal groups insist that the US is a secular institution, based on separation of church and state. Both are correct. Colonists and early European immigrants were overwhelmingly Christian, of various sects and movements. The Pilgrims ventured over largely to escape religious persecution, only to set up their own forms of religious intolerance toward other denominations. Jefferson and his allies noted this and insisted that religion be kept separate from government interference, and vice versa, and they prevailed.
Until very recently Protestants comprised the majority of the US population, with Roman Catholics not far behind. The influence of the traditional Protestant denominations has waned and their numbers have dropped sharply but some of the slack has been taken up by the growth of the evangelical sects whose pastors light up the passion, if not the intellect, of their flock. The fastest growing religious preference in the US is now “unaffiliated”. Whereas the RC Church has traditionally emphasized God's love and forgiveness of all us sinners through confession and penance, traditional Protestant doctrine emphasizes that God's chosen people can be identified by virtue of their good deeds. Both approaches have yielded a lot of good works and civil behavior by the faithful, and even by the not so faithful, who want to be seen in a good light by their peers.
Belief in the devil is now at an historic low and with scientists telling us ever more about our universe, faith in heaven and an afterlife is waning as well. It's become fashionable in liberal circles to speak badly of the Catholic Church, especially since the dreadful pedophile scandals emerged. Of course, most of the critics never set foot in a church. It remains to be seen if the major pedophile scandal in the football program at Penn State will unleash as virulent a protest again major intercollegiate sports programs, certainly a world every bit as venal and corrupt as the Church ever was, but one in which a fair number of both liberals and conservatives revel.
The two party system has served the country reasonably well for a long time. The Democrats have pushed for change and have championed labor unions in their struggles for a better deal for workers and have rallied round leaders such as FDR and Martin Luther King. Changes did happen. When the changes started to appear too rapid or frightening to a majority of the population, that middle slice of the voting public turned to the Norman Rockwell imagery of the country that gave us apple pie and Doris Day movies, which the Republicans like to conjure up as the real America. This back and forth worked to allow a degree of social change while avoiding radical dislocations.
Then, a few decades ago, things went badly wrong. The Democratic Party lost much of its base as immigrant groups worked their way up to suburban comfort and moved from aspiration to a defensive mode. American manufacturing disappeared to China and its former workers to unemployment or fast food outlets. Seeing how well GOP fund raising had gone in the financial world, Democratic party leaders decided to compete for support from Wall Street. This abdication left the traditional Democratic constituency, the workers and the poor, without meaningful representation, as the party decided to emphasize sexual issues and ignore economic problems. Meanwhile, control of the Republican Party moved from the prototype mid-west conservative banker/small businessman types to a new breed of sharks, trained at the Harvard School of Business to devise new ways to relieve grandmothers in California of their savings. Close colleagues included propagandists following the Josef Goebbels model. They were joined in their efforts by neo-cons (sometimes called neo-liberals) determined to bomb the world into acquiescence to American economic control. There was nothing either liberal or conservative about any of them. Neo-fascists might be a term closer to the mark, but fascists at least strove for an advanced industrial base. These people sought only reams of money for themselves and their cronies, while making the middle class an endangered species.
Throughout history, many people have opposed the Church but few have openly opposed the teachings of Christ, even when their actions ran counter to His words. Ayn Rand changed all that. There is no shortage of atheists in the world. Many seek an ethics based on the best philosophical thought rather than on fear of divine punishment. Ayn Rand was unique among atheists in not only opposing a belief in God but in turning the teachings of Christ on their head, preaching that greed is good, the masses should be left to their own miserable fate, while the elite should work for their own betterment and to hell with everybody else. She could and would be dismissed as a tedious, mediocre writer were it not for the fact that among her acolytes were people high in the Republican ranks such as Alan Greenspan, Ron Paul and Clarence Thomas. For a deeper analysis of this phenomenon, see Jeffrey Mikkelson's fine article.
Mitt Romney personified this school of thought in his remarks about the 47%. Nobody really knows what he represents because he's advocated on each side of every issue. However, the most telling clue may be in his selection of a sociopath vice-presidential running mate, Paul Ryan, the most avid Rand disciple on the American political scene, and the most consistent liar since Guinness kept records. Ryan also calls himself a Roman Catholic and recently said, with a straight face, that President Obama is leading the country away from Judeo-Christian values. Meanwhile he's concocted a budget that would throw grandma under the bus while exploding the deficit by giving additional massive cuts to his billionaire buddies, and curtailing most vital public services. A Catholic bishop even admonished him for a budget which was anything but Christian.
Evangelicals, who had some reservations about the Mormon Romney, love his science denials, and they're supporting Israel, no matter what, because the rapture, where Christ returns and carts off the true believers to heaven, won't happen unless and until Israel is safe in the Holy Land.
Lincoln's Republican Party may have been an ill-sorted bunch, but nothing compared to the present version. The party that claims to represent conservatives has everything except conservatives: neo-cons who would discard all international agreements the country has entered into; radical deregulators who have crashed the economy twice in this century and are ready to do it again; banksters; anti-tax zealots who would happily bankrupt the nation; traitors who publicly wished to see the government fail so they could take it over; science deniers; vulture capitalists, and even Roman Catholics who preach and live the anti-Christ dogma of Ayn Rand.