The U.N. agreed to the composition of the force and selected African generals but insisted on holding command.

The final resolution narrowed the circumstances under which the troops can use force: to protect themselves, aid workers and civilians. It also pledged that the force would not usurp the responsibilities of the Sudanese government.

For a period in the '90s, after 800,000 people were killed in the 1994 Rwandan genocide, and after Bill Clinton's 1998 apology for failing to intervene and stop it, there was much brighter line: Genocide was seen as something that demanded both immediate action and blame for inaction. The lesson of Rwanda helped make the ultimately successful case for action to halt the incipient genocide in the former Yugoslavia, even though it was not yet clear whether the ethnic cleansing there amounted to genocide. The idea was to err on the side of preventive intervention.

new "realism" about genocide that reflects the way the world has come to tolerate it: We now tacitly concede that in practice, we can't or won't do much more than deplore it and learn to live with it.

Samantha Power's important book on the subject was called A Problem From Hell.