Enlargement of the North Atlantic Treaty Organization (NATO) is the process of including new member states in NATO. NATO is a military alliance of twenty-eight European and two North American countries that constitutes a system of collective defense. The process of joining the alliance is governed by Article 10 of the North Atlantic Treaty, which allows only for the invitation of "other European States", and by subsequent agreements. Countries wishing to join have to meet certain requirements and complete a multi-step process involving political dialogue and military integration. The accession process is overseen by the North Atlantic Council, NATO's governing body.