NATO (North Atlantic Treaty Organization), or the North Atlantic Alliance for short, is a military intergovernmental grouping of 28 European and 2 North American countries. The defense budget for these countries in 2019 reached an incredible 57% of the defense budget of all countries in the world. But why and how did NATO come into being?
The history of the North Atlantic Alliance dates back to the first moments after World War II. It was clear to the devastated countries of Western Europe right after the war that they had to create a counterweight to the relatively aggressive policies of the Soviet Union. The following years proved them right, for example, in the form of the blockade of West Berlin, the February coup in Czechoslovakia, or pressure on countries under Soviet influence to reject Marshall's plan. Furthermore, these threats include a direct threat to the sovereignty of Norway, Greece and Turkey. 
Shortly after the end of the war, Western countries began to reduce their defence establishments and demobilize forces under the convention. However, the Soviet Union clearly did not want to proceed with demobilization. In response to the threat of the emerging Eastern Bloc, Belgium, France, Luxembourg, the Netherlands and the United Kingdom signed the so-called Brussels Treaty in 1948. These countries immediately entered into a dialogue with the United States, Canada, Denmark, Iceland, Italy, Norway and Portugal. The result was the adoption of the Washington Treaty in April 1949.
During the Cold War, the influence of the North Atlantic Alliance grew in importance. In 1952, Greece and Turkey joined NATO, and in 1955, West Germany. It was the accession of West Germany to NATO that led to the creation of the Soviet counterweight to NATO, the so-called Warsaw Pact. Spain joined NATO in 1982, the Czech Republic, Hungary and Poland in 1999, Bulgaria, Estonia, Lithuania, Latvia, Romania, Slovakia, Slovenia in 2004, followed by Albania and Croatia in 2009, Montenegro in 2017 and finally in 2020 in Northern Macedonia.