In the future development of the law, the June 1967 war would have its greatest impact on the issue of an attack in anticipation of an attack by another state. The perception, albeit inaccurate, that Israel reacted to an expected imminent attack would impact international practice on the scope of self-defense. Situations arising in later years would involve less often a claim that an army was about to march across a border than a claim that military elements based in another state were preparing to launch attacks of a lesser order. Asymmetrical war became the more typical background for a claim. In this context the phenomenon of an assertion of the need to use force in anticipation would gain a prominence not seen earlier. The June 1967 war provided a ready, if flawed, reference point. The June 1967 war was a turning point in anticipatory self-defense.

Anticipatory Self-Defense before 1967

For the interwar years, Brownlie found little support for self-defense in anticipation. The UN Charter, dating from 1945, allowed, by its Article 51, for defensive force only if an “armed attack occurs.” The United Nations was to ensure the peace. If attacked, a state could defend itself, but it had to report immediately to the Security Council and abide by what the council might decide. Between 1945 and 1967, no situation arose in which a state using force said it was preempting force by the other state. Gray points out, as an indication of the frailty of the doctrine of anticipatory force, that states have been reluctant to invoke it.