Live Updates: Russia’s war in Ukraine

A soldier with the Polish Army sits in a tank as a NATO flag flies behind him during military exercises in 2015 in Zagan, Poland. (Sean Gallup/Getty Images)Finland – which shares an 800-mile border with Russia – is one step closer to joining NATO after the nation’s president and prime minister announced their support for being a part of the US-led military alliance. The Kremlin said the move would be a threat to Russia.Here’s what you need to know about NATO and how it works:NATO is a European and North American defense alliance that was created as the Cold War escalated and is headquartered in Brussels, Belgium. The aim of the alliance was to protect Western European countries from the threat posed by the Soviet Union and to counter the spread of Communism after World War II.Remember: An armed attack against one or more of them in Europe or North America shall be considered an attack against them all. Article 5 of the North Atlantic Treaty guarantees that the resources of the whole alliance can be used to protect any single member nation. This is crucial for many of the smaller countries who would be defenseless without its allies. Iceland, for example, has no standing army. Since the US is the largest and most powerful NATO member, any state in the alliance is effectively under US protection.The alliance started with 12 founding countries, but over the decades since, the alliance has grown to include a total of 30 members.In alphabetical order, they are: Albania, Belgium, Bulgaria, Canada, Croatia, Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxemburg, Montenegro, the Netherlands, North Macedonia, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Turkey, the UK and the US.Ukraine is not a member of NATO, but has long hoped to join the alliance. This is a sore point for Russia, which sees NATO as a threat and vehemently opposes the move.Amid ongoing tensions with the West, Russia has asked for iron-clad guarantees that the alliance won’t expand further east — particularly into Ukraine.But the US and NATO have resisted those demands. The alliance has always had an “open door policy,” which states that any European country ready and willing to undertake the commitments and obligations of membership is welcome to apply for membership. Any decisions on enlargement of the alliance must be agreed unanimously.Following the end of the Cold War, NATO made it clear it would welcome expansion to the east and in 1997, Czech Republic, Hungary and Poland were invited to begin accession talks.Since then, more than a dozen countries from the former Eastern bloc, including three former Soviet republics, joined the alliance.Read the full explainer on NATO here and see a map of its current members below: