Why did president roosevelt and prime minister churchill want to create the declaration on liberated europe

 President Roosevelt and Prime Minister Churchill wanted to create the Declaration on Liberated Europe which was expressed in a sentence "the right of all people to choose the form of government under which they will live." due to preserve European countries (mainly Poland) from the taking over by Stalin

The league of nations was found in 1919 to keep peace after world war l.but it failed to prevent world war ll in 1939,so in 1945 the nations of the world set up a new organization,the united state (un).since then, the un has encouraged international cooperation and worked to resolve conflict