Tony Blair’s April 1999 Chicago speech is widely seen as foreshadowing his later decision to support the invasion of Iraq. Two sets of context for the speech are described: other criteria for the use of force, going back to the Just War tradition and more recent contributions from Caspar Weinberger and Colin Powell, and the December 1998 strikes against Iraq and the Kosovo War, which began in March 1999. The origins of the five factors mentioned when considering force are explored and their implications assessed.