The Ten Year Rule belonged to a postwar belief that the First World War had discredited war as an ordinary instrument of policy. Security guarantees, agreements renouncing aggressive war, and the League of Nations appeared to offer a system in which disputes could be settled collectively. The League, however, had no independent power to enforce its decisions. Member states might have to wage war to uphold rules created to prevent war, which exposed a basic weakness in collective security.
Notable Point · 6:07-7:17
Why League enforcement could require war
Post-1918 hopes that treaties and the League would prevent another war ran into a basic problem: collective rules still depended on member states being willing to enforce them.