Why did the League of Nations Assembly usually require unanimous decisions?

The requirement for unanimity in the League of Nations Assembly was a constitutional feature established by the Covenant of the League of Nations. Under this rule, every member delegation held the power to veto a decision, as the Assembly’s formal actions required the agreement of all members who cast a vote.1

This structure was designed to ensure that international decisions respected the sovereignty of member states. In practice, however, the League developed a workaround to avoid gridlock: delegations that disagreed with a majority proposal would typically voice their opposition during committee meetings and then abstain from voting when the matter reached the plenary Assembly, thereby allowing the decision to pass without their formal dissent. While the veto power existed in theory, actual deadlocks were exceedingly rare.1