Belgium is a founding member of NATO of 1949 and hosts its headquarters in Brussels
Background
Belgium's capital is in the news as the seat of European decision-making, and it is also the home of the North Atlantic Treaty Organization. NATO's own member list records Belgium's accession in 1949, the year the alliance was founded, which makes it one of the twelve original parties to the North Atlantic Treaty. NATO states that its headquarters is in Brussels, Belgium. The alliance now has 32 member countries. The most recent to join were Finland in 2023 and Sweden in 2024.
In plain words
NATO North Atlantic Treaty Organization — A military alliance of North American and European states founded in 1949.