Divide and Rule
Keeping a subject population fragmented and turned against itself so it cannot unite against the ruler. Modern empires refined it; its fault lines still bleed.
The cheapest way to rule people who outnumber you is to make sure they never act as one. Divide and rule, from the Latin divide et impera, is the strategy of keeping a large subject population split into rival factions so that its energy is spent fighting each other instead of the ruler standing above them all. The phrase has been pinned on everyone from Philip II of Macedon to Julius Caesar to Machiavelli, but it names something older than any of them, and, unfortunately, newer too.
From Rome to the Raj
The Romans practiced it as deliberate statecraft, cutting favorable deals with some tribes and cities while crushing others so that no coalition could form against the legions. But the method reached industrial scale under modern empires, above all the British, who governed hundreds of millions of people with a strikingly thin layer of officials and soldiers. The leverage came from turning a population into a set of fixed, countable categories and then playing them against one another. British India ran a decennial census that sorted a fluid society into rigid boxes of religion and caste. The administration elevated favored groups as intermediaries, recruited its soldiers and clerks disproportionately from chosen 'martial races' and minorities, and eventually granted separate electorates so that Hindus and Muslims voted as blocs. The colonial state did not invent Hindu, Muslim, or Brahmin, but it froze them, counting and privileging until soft boundaries became hard walls. Identities that had been local, overlapping, and negotiable hardened into national ledgers.
Lines drawn to last
The strategy's most lethal feature is that it outlived the empires that used it. In India, decades of communal engineering culminated in the 1947 Partition: as the British withdrew, the subcontinent was split into India and Pakistan, unleashing violence that killed hundreds of thousands and displaced some fifteen million people in a matter of months. In Rwanda, Belgian administrators turned the once-flexible categories Hutu and Tutsi into a racial hierarchy and stamped ethnicity onto identity cards; that codified division helped make possible the 1994 genocide, in which roughly 800,000 people were killed in a hundred days. Across the Middle East and Africa, borders drawn to trap rivals inside one state, or to sever natural partners, still feed the sectarian and tribal conflicts that outside powers once found so convenient.
The long echo
Empires favored the tactic because it was cheap. A garrison hopeless against a united population can hold indefinitely against a fragmented one, especially when the fragments police each other. That is also why the damage lingers long after the flag comes down. Census categories became identities; identities became grievances; grievances became the organizing lines of post-colonial politics. The point was rarely hatred for its own sake. It was administrative economy, and hatred was the byproduct that made the economy work. Rulers who inherited these states often found the same tool waiting in the drawer and used it themselves. The empires that drew the lines are mostly gone. The lines, and the habit of governing through them, are not.