A ruler weakens a larger opposition by setting its factions against one another.
Roman practice, and the standing method of every occupying power since. Its cost is that the divisions outlast the ruler, which is the standard explanation for post-colonial boundary conflicts.
In practice
- An employer facing a union negotiates separately with two grades and offers each a slightly better deal than the other.
- A committee's opposition is split by giving one faction a small win, and the two halves never rejoin.