NATO, explained: Why the alliance was formed — and what it's doing for Ukraine

NATO is the North Atlantic Treaty Organization. It's a military and political alliance that was founded in 1949 in response to the actions of the Soviet Union.

"The Allies in the West began to see that the Soviets were trying to take their advantage after World War II," seeking to turn countries in Central and Eastern Europe into "satellite nations" of the Soviet Union, Jim Townsend, who served as deputy assistant secretary of defense for Europe and NATO during the Obama administration, tells NPR.

Townsend, who spent 30 years at the Pentagon, says during the earliest days of the Cold War, it was obvious that Russia was going to be very aggressive. So the European allies came together and asked the U.S. to join a new alliance.

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