CHICAGO (CBS) — With the start of the NATO summit in Chicago just a few days away from beginning, here is a look back at the beginnings of the multinational alliance.

President Harry S Truman signed the North Atlantic Treaty in 1949 forming the North Atlantic Treaty Organization. The signing came just a year after the Communist takeover of Czechoslovakia and not long after World War II.

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The aim of the U.S. and its European allies was to stand firm against totalitarian Communism and promote democracy.

“If there is anything certain today, if there is anything inevitable in the future, it is the will of the people of the world for freedom and for peace. Men with courage and vision can still determine their own destiny. They can choose slavery or freedom, war or peace,” said Truman.

The initial 12 member countries included Belgium, Canada, Denmark, France, Britain, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal and the United. They agreed that NATO’s mission would be to safeguard the freedom and security of its members through political and military means. And they agreed in the Treaty’s Article 5 that “an armed attack against one or more of them…shall be considered an attack against them all.”

The Cold War with Soviet nuclear escalation tested NATO but by 1989, revolution began and communism began to crumble.

“Our opportunity is clearly is to bring the world closer to our vision-open borders, more freedom, less weapons and the rule of law. We are reaching out to Eastern Europe and the Soviet Union. Our most important task remains the prevention of war,” said Manfred Wörner, then NATO Secretary General.

By 1993, NATO extended its hand to former Warsaw Pact members and by 2002 seven former Eastern Bloc countries — Lithuania, Estonia, Latvia, Bulgaria, Romania, Slovakia and Slovenia — were invited to join. NATO invited Croatia and Albania to join in 2008.

“NATO continues to serve as the main forum where the West can formulate and coordinate common political decisions. Under its umbrella the dynamism of European unification can unfold,” said Willy Claes, then NATO Secretary General.

It would be the mid 1990’s before NATO took its first wartime action in the Bosnian War. NATO intervened again during the Serbian crackdown on Albanian civilians in Kosovo.

Military might would be needed again after the 9/11 attacks when NATO invoked Article 5 for the first time in its history and joined the U.S. in attacking Afghanistan.

Now for the first time, there’s no clear enemy. NATO’s 28 member countries will use the Chicago summit to prepare for new threats and challenges.

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