Why did Christian Lous Lange deserve the Nobel Peace Prize in 1921?

Norwegian Christian Lous Lange championed internationalism — the idea that countries could work together diplomatically to solve international problems and create peace through collective security. The first successful attempt to put the ideals of internationalism into practice was the Inter-Parliamentary Union (IPU), a neutral forum for multilateral negotiation founded in 1889, and Lange was one of its leading figures. Besides Lange, seven other IPU personalities would go on to win the Nobel Peace Prize.

During World War I, when the Germans overran the IPU's headquarters in Belgium, Lange installed the headquarters in his own home in Oslo. His dogged efforts kept the IPU alive during the war, when many international organizations died.

World War I revealed in more concrete terms what governments could do if they worked together — both for good and for ill. After the war ended, President Woodrow Wilson fought for and founded the League of Nations to bring together the governments of the world so that a war on that scale would never be fought again. For his hard work, Wilson received the Nobel Peace Prize in 1920. (Ironically, the United States never joined the League of Nations because of opposition in the Senate.) Lange was active as a Norwegian delegate to the League of Nations and was especially active in the area of disarmament.

For his relentless efforts to promote peace through international cooperation and diplomacy through the Inter-Parliamentary Union, the League of Nations, and various other organizations (including the Nobel committee itself), he was jointly awarded the 1921 Nobel Peace Prize with Karl Hjalmar Branting.