Although in some cultures there upward mobility gives people hope to change their futures, statistically a person born into poverty is likely to die there and have children who live powerless as well.
The current economy in the United States is one that has divided the rich and the poor, with the rich taking the bulk of the gains in productivity of the last several decades. According to Paul Krugman in a recent article titled For Richer in the New York Times about the distribution of wealth, there is even more of a divide between the classes today than in the 1920s, meaning that the disadvantaged are becoming more so (and the middle class may be headed their way as well).
Most of the most truly disadvantaged people live in the developing world with no running water, electricity or sanitation.
A current problem for the richest nations is the fact that many terrorists come from parts of the world where they have limited opportunities for advancement.