It means “divide and rule”. It describes the type of political attitude widely diffused in history, which is to stir up divisions between peoples to avoid their coalition against the established power. It is hard to tell with precision the paternity of motion, that according to some sources go back to Philippe Macedone, but according to others it comes from different Roman imperators (which may seem more plausible, since the expression is in Latin indeed, and moreover it was the political rule that Roman Empire pursued on colonized territories). Another powerful example comes from the times of Louis XI in France, which used to say “diviser pour règner” (French), which put in the contrast between each other the feudatory in France to keep better control over them.