The North Atlantic Treaty Organization(NATO) was founded in 1949 and evolved to protect the West from the USSR. The USSR established its own organization called The Warsaw Pact to protect its allies in Europe. The Warsaw Pact collapsed when the USSR collapsed in 1989-91. Though the enemy split into countries the NATO survived and continues to evolve to combat present and future attackers.

From its original inception the NATO has added new members and today 29 countries are members of this powerful military alliance as shown in the infographics below:

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Source: Sputnik News