By design the United Nations cannot stop the war in Ukraine. The world body chartered in 1945 to promote peace and cooperation has a decidedly mixed record in those areas, but that is mostly because the great powers from the start kept for themselves the authority to sanction or veto international efforts to prevent war. In this episode, Karen Mingst, an expert on diplomacy and global governance, explains where the U.N. has been effective in building a better world, and where it has failed to live up to its principles.