I think the US being more conservative is really fairly recent (post WW2) on most issues. Except for anything having to do with that 800 pound gorilla of the US social landscape, racism.
I actually read a really interesting book about this that I grabbed in Canada over the holidays (currently not available in the US). It's called "Fire and Ice: The United States, Canada, and the Myth of Converging Values". Basically it's written by a Canadian market research/polling guy. In the process of doing his job, he noticed that the politics and values of Canadians and Americans have actually gotten more different over the past couple of decades, not more similar. Which is really surprising considering that Canadians watch more and more American movies/TV shows, we're sharing the same internet, free trade is increasing commerce between the two countries, etc. Basically you have a trend where the US is going one way and much of the rest of the western world is going another way - even Canada which is right next to it and shares much of the same mass media.
As for what the changes are, there's really two aspects to it. One is that the US has completely swapped places on the political/social map with some other countries, especially Canada. "Fire and Ice" points out that half a century ago, the suggestion that Canada was more liberal than the US would have been ludicrous. Canada had a more rural population, probably less ethnic diversity/immigration, people went to church more, and in general Canadians would tell you their politics were more "peace, order, and good government" compared to the freedom-loving/libertine US. It's only recently that Canada and the US have completely swapped places. Now Canada is highly urban, has a much higher immigration rate than the US, religion is way less of a big deal than the US, and public attitudes have totally liberalized. In the US in the 60s and early 70s there was a shift toward more liberal opinions to the point people were confidently predicting legalized pot, an equal rights amendment for women, etc. Then abruptly that all stopped and there was a swing back to the right - whereas in Canada, no such thing.
But the REALLY surprising thing about the US swing towards conservatism - surprised me and I know a lot about opinion research - is how much of it happened during the 1990s. The point where Canada and the US "crossed over" and Canadian attitudes finally became identifiably more liberal than US attitudes was in the 80s, not surprising as this was the Reagan era, the "me" decade in the US. But during the 1990s - when Clinton was president, everybody was prosperous, and things were pretty peaceful - the US continued to make a big beeline away from liberal opinions, whereas Canada continued to become more liberal. So you can't really blame this on who is president or on international conflicts. US society was moving away from liberal opinions even after the Cold War was over and before September 11.
As for the specifics of this "move away from liberalism" that's interesting too. Because really there are two trends in the US. One trend is that the religious right has gotten a lot more influence over the past couple of decades - more political power, its own media, and so on. But this growing political power of "traditional conservatism" doesn't mean growing numbers of people believing in it. No matter how much louder and more unified the fundamentalists and hard right types get, they're not really getting more numerous. Also, the progressive/liberal "wouldn't vote for a Republican with a gun to my head" crowd isn't really getting much smaller. The big change is happening in the center - the approximately half of the population that isn't committed to the hardcore right or left.
And what's happening to the center is something that shouldn't bring any comfort to either the right or the left. "Fire and Ice" uses statistical techniques to measure the most important trends of change in US social/cultural attitudes. Their technique produces a two-dimensional political map.
One dimension is authority vs. individuality. People high on authority place emphasis on duty, behaving according to social norms, obedience to authority, traditional religion/families, and so on. People high on individuality place emphasis on questioning authority, non-hierarchal organization, sexual permissiveness, equal/flexible relationships between people of different ages and genders, and so on.
The other dimension is survival vs. fulfillment. People high on survival see the world as a sort of Darwinian struggle - survival of the fittest, you've got to look out for your own first, other people are ready to take advantage of you, you need to look out for your security and wealth, etc. People high on fulfillment emphasize cooperation and social connection with others. Be a contributor to the community, money doesn't mean everything, and so on.
The traditional left in the US is high on individuality and fulfillment. The traditional right is high on authority and survival. But these guys aren't where the change is taking place. The center is shifting from high authority, high fulfillment people (generally conventional but believing in community and harmony), to high individuality, high survival people (reject traditional authority, but also reject community and believe it's a dog eat dog world).
This is actually a really troubling trend. It's not a shift towards liberalism or conservatism as we conventionally recognize them. It's people rejecting both the conservative solution to social problems (obey the rules of authority and convention) and the liberal solution (cooperate with others, tolerate differences, and form communities). They are out for themselves, they measure success by material gain, and their position on social problems is that shit happens. This is radically different from the rest of the western world, where populations have been predominantly shifting toward liberalism, rather than towards nihilism (for lack of a better word).
Specifically, some the attitudes that have shown the most dramatic increase in the US in the 90s are:
Sexism
- 49% of Americans believe that men should be heads of their household in 2000, up from 42% in 1992. Canadian number is 18%.
- 38% of Americans believe that men are naturally superior to women in 2000, up from 30% in 1992. Canadian number is 24%.
Xenophobia/Nationalism
- 25% of Americans in 2000 believed that non-whites should not be allowed to immigrate, up from 16% in 1992. Canadian number is 13%.
- 49% of Americans believe immigrants have a good influence on the country, compared to 77% of Canadians. (43% of Americans believe immigrants have a bad influence, the other 8% would be neutral/undecided).
- In 2000 31% of Americans said they enjoyed showing foreigners that they're smarter and stronger, up from 27% in 1992. Canadian number is 14%, down from 17% in 1992.
Acceptance of violence
- 24% of Americans think violence is a normal part of everyday life in 2000, up from 10% in 1992. Canadian number is 12%.
- 31% of Americans in 2000 believe that when you're frustrated, a little violence is no big deal and can offer relief, up from 14% in 1992. Canadian number is 14%.
- 23% of Americans believe violence is an acceptable way to reach one's goals in 2000, up from 9% in 1992. Canadian number is 13%.
Acceptance of advertisement
- 44% of Americans in 2000 believe that a widely advertised product is probably good, up from 34% in 1992. Canadian number is 17%.
- Increasing portion of Americans report getting great pleasure from advertising (decreasing portion in Canada)
Materialism
- Increasing portion of the US population believes it's important that others admire the things you own, decreasing portion feel a personal responsibility to those worse off than themselves, increasing portion say they have trouble accomplishing things due to a hectic life, increasing portion say they need to get away from the burdens of their lives. All trends in Canada are the opposite.
Decreasing civic engagement ("Bowling Alone" effect)
- In 2000, 34% of Americans discuss local problems with other people, down from 66% in 1992. Canadian number is 47% (down slightly from 52%).
- Average American spends 40% of their leisure time watching TV, up from 30% in the 1960s. Canadian number was 30% then and now.
- 31% of Americans are obese compared to 15% of Canadians
- SUVs outsell minivans 2:1 in the US, minivans outsell SUVs 2:1 in Canada. (Market research shows that people view the minivan as a symbol of family commitment, whereas SUV owners don't want to be "tied down" and don't want other people to see them as having lost the adventure in their lives).
Those are some of the most noteworthy changes. There are other changes. Some are negative (such as a noticable 1990s increase in "ecological fatalism", the belief that environmental problems cannot be fixed). A few are positive (people feel more comfortable with adapting to a complex society, have more support for flexible family structures, and have more support for the ideal of multiculturalism even while they are in fact becoming more hostile to immigrants).