Why it is difficult to pit one group of people against the other?

If social differences cross cut one another, it is difficult to pit one group of people against the other. It means that groups that share a common interest on one issue are likely to be in different sides on a different issue. Consider the cases of Northern Ireland and the Netherlands. Both are predominantly Christian but divided between Catholics and Protestants. In Northern Ireland, class and religion overlap with each other. If you are Catholic, you are also more likely to be poor, and you may have suffered a history of discrimination. In the Netherlands, class and religion tend to cut across each other. Catholics and Protestants are about equally likely to be poor or rich. The result is that Catholics and Protestants have had conflicts in Northern Ireland, while they do not do so in the Netherlands. Overlapping social differences create possibilities of deep social divisions and tensions. Cross-cutting social differences are easier to accommodate.