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

As Russia continues its attack on Ukraine, the role of NATO is at the forefront.

Here's a quick overview of the alliance, the role that the United States plays within it, and what it's doing to help Ukraine amid Russia's invasion.

What is NATO and why was it created?

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.

The result was NATO. Retired American general and future U.S. president Dwight Eisenhower was tapped to be NATO's first military leader: the Supreme Allied Commander Europe.

In 1955, the Warsaw Pact was formed by the Soviet Union and seven Eastern bloc nations as a collective defense treaty in response to NATO.

Which countries are in NATO?

There were 12 founding members of the alliance in 1949: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom and the U.S.

The alliance has expanded over time, and its membership now numbers 30. The other nations are Greece, Turkey, Germany, Spain, the Czech Republic, Hungary, Poland, Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, Slovenia, Albania, Croatia, Montenegro and North Macedonia.

Three additional countries have declared their desire to join the alliance: Bosnia and Herzegovina, Georgia and Ukraine. Membership is officially open to any "European State in a position to further the principles of this Treaty and to contribute to the security of the North Atlantic area." The decision to invite a country to join NATO is made by consensus of the member nations.

Ukraine has not entered NATO — essentially because of Russia's opposition to it, and the conflict that its admission would cause.

What are members' responsibilities to each other?

NATO's Article 5 spells out its key principle of collective defense: If any member of the alliance is attacked, it shall be considered an attack on all members.

And if such an armed attack does occur, each member will take the actions it deems necessary to assist the ally attacked, "to restore and maintain the security of the North Atlantic area." What assistance is provided is determined by the individual country, in concert with the other allies. The assistance doesn't necessarily have to be military.

Article 5 has been invoked just once: Following the terrorist attacks on the U.S. on Sept. 11, 2001. NATO launched its first ever anti-terror operation, to help patrol the skies over the U.S. The alliance also sent patrols to the Mediterranean to detect and deter terrorist activity.

Even without invoking Article 5, NATO has taken collective defense measures several times, including in Syria and now with the Russian attack on Ukraine.

Townsend likens NATO's role as hosting a potluck for member nations, and asking each to bring something in particular to the picnic. Otherwise "everyone would just bring potato chips, because that's the cheapest thing."

What has been NATO's relationship with Russia until now?

There was a time in the 1990s when it was thought that Russia might potentially join NATO at some point, says Townsend, as countries like the Czech Republic, Hungary and Poland were preparing to enter the alliance. But Russia's trajectory changed in the 2000s, and that never happened.

NATO's relations with Russia deteriorated in 2014, when Russia illegally annexed Crimea. Practical cooperation between the alliance and Russia has been suspended since then, though political and military channels of communication remain open.

How is NATO structured as a military force?

NATO's multinational Response Force is composed of troops from member nations. Troops wear their own country's uniform, and individual military units are headed by leaders from those units' home countries.

The Supreme Allied Commander is at the top of the chain of command. An American is always in this role, says Townsend, "because we bring most of the toys." His or her deputy is usually a Brit and the chief of staff is usually a German, Townsend says.

Why is Russian President Vladimir Putin opposed to Ukraine's desire to join NATO?

Putin has said he regards Ukraine as a part of Russia.

"The idea that Ukraine would actually establish relationships — like a nation would — to the European Union and NATO, that upsets in his mind this idea that Ukraine is Russia, Russia is Ukraine," says Townsend.

Robert Pszczel, a former Polish diplomat and a former NATO official, says that one of Putin's obsessions is Russia's role in the global order. "He believes that Russia has the right, because it's a big power, to dictate to other countries," he tells NPR. "Just the very existence of NATO creates a problem for Putin because NATO stands for collective security and stands for upholding that international order."

The Russian president has also expressed concern that if Ukraine joins NATO, the alliance would put pack Ukraine full of weapons – and be within striking distance of Moscow. "In creating a threat for Russia, Ukraine creates a threat for itself," Putin said last month.

Several countries bordering Russia are already part of NATO: Estonia and Latvia. Lithuania and Poland border the Kaliningrad region, the chunk of Russia on the Baltic Sea.

What is NATO doing for Ukraine?

NATO has been amassing battalion-size "battlegroups" in countries along the alliance's eastern flank in Estonia, Latvia, Lithuania and Poland. These forces are prepared for combat and are led by the United Kingdom, Canada, Germany and the U.S., respectively. The alliance has sent planes and ships to NATO territory in eastern and southeastern Europe, and there's a multinational brigade in Romania.

Last week NATO announced it would create four new battlegroups in Hungary, Slovakia, Bulgaria and Romania.

The alliance has also been providing huge amounts of weapons and equipment to Ukraine.

So far, the alliance has not met one repeated request by Ukrainian President Volodymyr Zelenskyy: to impose a no-fly zone. That's because NATO fears that doing so would lead to direct combat with Russia, widening the conflict into a regional war and potentially even a third World War.

The U.S. has provided Ukraine with anti-aircraft weapons, though, which can can be used to shoot down aircraft and cruise missiles.

The alliance is likely also providing help in ways it isn't talking about. "Not everything should be advertised, for security reasons," Pszczel says.

Some wonder why NATO isn't giving Ukraine everything Zelenskyy asks for. A recent NPR/Ipsos poll found that 39% of Americans think the U.S. should be doing more when it comes to the war in Ukraine.

NATO is doing as much as the politics of its members currently allow, Pszczel says: "These are free nations, democratic nations, and they all have to agree on things. At the moment, there is no consensus. There's not willingness to go a step or two step further and essentially send troops or enter into direct military confrontation with Russia."

But public opinion is a powerful force, he says, and there is a strong moral opposition in NATO countries to Russia's attack on Ukraine.

If Putin's war continues, might consensus be reached to take NATO's involvement to the next level? "Time will show," says Pszczel.

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