In the decades surrounding the turn of the twenty-first century, the limits of anticipatory self-defense would be pushed in connection with a series of incidents of use of force. One direction of expansion was toward uses of force that fall under the category of reprisal. Reprisal is a use of force undertaken in response to a prior use of force but where that prior use of force is no longer ongoing. The UN Charter, by limiting the rationale for unilateral use of force to self-defense, is generally thought to outlaw reprisals. Per Ian Brownlie, “There is a general assumption by jurists that the Charter prohibited self-help and armed reprisals.” And Derek Bowett: “Under the Charter of the United Nations, the use of force by way of reprisals is illegal.” In one resolution, the Security Council said that it “condemns reprisals as incompatible with the purposes and principles of the United Nations.”

Self-Defense or Reprisal?

In 1986, the United States bombed targets in Libya at Benghazi and Tripoli, following a deadly explosion at a Berlin nightclub frequented by US military personnel. The United States held Libya responsible for the explosion. Britain assisted by allowing US aircraft to depart from its air bases. Asserting self-defense, the United States claimed that Libya planned future attacks against US objectives abroad. The United States understood that without a claim of future attacks, the action would be a reprisal, since the Berlin attack was not ongoing. To this extent, the United States was asserting anticipatory use of force. Libya complained to the United Nations.