In John F. Kennedy's inaugural address, given on January, 20, 1961, he actually calls the United Nations "our last best hope." Here is the excerpt from the speech, taken from the website of the JFK Library (www.jfklibrary.org; the link is below):
"To that world assembly of sovereign states, the United Nations, our last best hope in an age where the instruments of war have far outpaced the instruments of peace, we renew our pledge of support--to prevent it from becoming merely a forum for invective--to strengthen its shield of the new and the weak--and to enlarge the area in which its writ may run."
In this portion of the speech, Kennedy said that the United Nations was a way to prevent war, and he renewed our nation's commitment to the United Nations as a way to protect weak nations. He hoped to end the use of the United Nations as "a forum of invective," or a place merely for nations to air their grievances.
Much of the rest of the speech is a promise to fight communism, as the United States was then involved in fighting the Cold War against the Soviet Union and other nations. Kennedy said, "Let every nation know, whether it wishes us well or ill, that we shall pay any price, bear any burden, meet any hardship, support any friend, oppose any foe to assure the survival and the success of liberty." Although he does not mention communism directly, no one in the audience at the time would have had any doubt that he was referring to fighting the Cold War.
Kennedy's inaugural address is perhaps, however, best remembered not only for its eloquence and fine delivery but also for its call to social action. At nearly the end of the speech, Kennedy said, "And so, my fellow Americans: ask not what your country can do for you--ask what you can do for your country." In other words, Kennedy was calling, in words that have often been re-quoted, for Americans to give of themselves to their country to make it great.