I think that there are lots of contributing factors to the US keeping social peace. I was trying to think of “the one” but cant, there are too many that keep flip flopping for me, so I will list a few.

1. “The American dream” as mentioned already is a big one. Knowing that you can be more than you are if you work at it and seeing examples is inspirational.
2. Distractions. Anyone unhappy with something/anything can quickly forget their woes by watching TV, radio, games, sports, etc. (drugs, alcohol, sex, etc.)
3. Physical security. Although not as safe as we sometimes think we are, the fact that most of America has a low crime rate and we don’t worry about invasion from Canada makes us feel safe.
4. Financial security. No one likes to be in the poor house but we know no matter how bad we screw up our finances there is always a way to get them fixed. Credit cards, bankruptcy, welfare, etc.
5. Selfish. I think that in general, Americans are selfish and unless they are directly effected by some kind of outrage they wont act. Taking care of their own business is priority #1, weather it is school, work, family whatever there is not enough time in the day to do everything we “need” to do, who has time to be part of a revolution or cause. Which leads me to the most important #.
6. Independent. Americans are fiercely independent and even when organized in a group it quickly fractures when pushed. We don’t like to be told what to do. The biggest reason IMO that we haven’t had a major revolution or reform is because we are free thinking independent people. If there are 100 people who all want reform there will be 100 different ideas of what that reform will be, then nothing gets done. When we do organize and move toward a goal it usually doesn’t last and we go back to our own agendas after an easy solution is found.

Unless there is a MAJOR event to threaten our way of life, we will always have social peace. It’s just too much work to have anything else.