NATO, North Atlantic Treaty Organization

Headquarters of NATO is Brussels, Belgium

There are 30 members NATO. 

There were 12 founding members in 1949:

Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, Netherlands, Norway, Portugal, United Kingdom, United States,

The other member countries are:

Greece (1952), Turkey (1952),  Germany (1955), Spain (1982), Czech Republic (1999), Hungary (1999), Poland (1999), Bulgaria (2004), Estonia (2004), Latvia (2004), Lithuania (2004), Romania (2004), Slovakia (2004), Slovenia (2004), Albania (2009), Croatia (2009), Montenegro (2017), North Macedonia (2020)