Why was the United Nations Security Council able to authorize military action in the Korean War?

The United Nations Security Council was able to authorize military action in the Korean War because the Soviet Union was absent during the critical vote.1

At the time, the Soviet delegate was boycotting the Security Council meetings to protest the fact that the People’s Republic of China lacked representation in the United Nations. Because the Soviet Union was not present to exercise its veto power, the Security Council was able to pass resolutions condemning the invasion of South Korea and calling upon member nations to provide military assistance to restore peace. This allowed for the creation of a unified command under General Douglas MacArthur to resist the aggression.1