Divide and rule (or divide and conquer, from
Latin dīvide et imperā) in
sociology is gaining and maintaining
power by breaking up larger concentrations of power into pieces that individually have less power than the one implementing the strategy. The concept refers to a strategy that breaks up existing power structures, and especially prevents smaller power groups from linking up, causing rivalries and fomenting discord among the people.
Traiano Boccalini cites "divide et impera" in La bilancia politica
 as a common principle in politics. The use of this technique is meant to empower the sovereign to control subjects, populations, or factions of different interests, who collectively might be able to oppose his rule.
Machiavelli identifies a similar application to military strategy, advising in Book VI of The Art of War
 (Dell'arte della guerra),
 that a Captain should endeavor with every art to divide the forces of the enemy, either by making him suspicious of his men in whom he trusted, or by giving him cause that he has to separate his forces, and, because of this, become weaker.
The maxim divide et impera has been attributed to
Philip II of Macedon, and together with the maxim divide ut regnes was utilised by the Roman ruler
Caesar and the French emperor
The strategy, but not the phrase, applies in many ancient cases: the example of
Gabinius exists, parting
the Jewish nation into five conventions, reported by
Flavius Josephus in Book I, 169-170 of The Wars of the Jews (De bello Judaico).
Strabo also reports in Geography, 8.7.3
 that the
Achaean League was gradually dissolved under the Roman possession of the whole of
Macedonia, owing to them not dealing with the several states in the same way, but wishing to preserve some and to destroy others.
The strategy of division and rule has been attributed to sovereigns, ranging from
Louis XI to
Edward Coke denounces it in Chapter I of the Fourth Part of the Institutes, reporting that when it was demanded by the
Commons what might be a principal motive for them to have good success in
Parliament, it was answered: "Eritis insuperabiles, si fueritis inseparabiles. Explosum est illud diverbium: Divide, & impera, cum radix & vertex imperii in obedientium consensus rata sunt." [You would be insuperable if you were inseparable. This proverb, Divide and rule, has been rejected, since the root and the summit of authority are confirmed by the consent of the subjects.] On the other hand, in a minor variation,
Sir Francis Bacon wrote the phrase "separa et impera" in a letter to
James I of 15 February 1615.
James Madison made this recommendation in a letter to
Thomas Jefferson of 24 October 1787,
 which summarized the thesis of
 "Divide et impera, the reprobated axiom of tyranny, is under certain (some) qualifications, the only policy, by which a republic can be administered on just principles." In Perpetual Peace: A Philosophical Sketch by Immanuel Kant (1795), Appendix one, Divide et impera is the third of three political maxims, the others being Fac et excusa (Act now, and make excuses later) and Si fecisti, nega (when you commit a crime, deny it).
Elements of this technique involve:
- creating or encouraging divisions among the subjects to prevent alliances that could challenge the sovereign
- aiding and promoting those who are willing to cooperate with the sovereign
- fostering distrust and enmity between local rulers
- encouraging meaningless expenditures that reduce the capability for political and military spending
Historically, this strategy was used in many different ways by empires seeking to expand their territories.
The concept is also mentioned as a strategy for market action in
economics to get the most out of the players in a competitive market.