member countries; member states
Refers to the countries that are members of an international organization, treaty, or similar body. Often used in formal or diplomatic contexts.
Member countries must ratify the treaty.
The member states of the UN participated in the conference.
加盟国 is a more general term for a member country, while 加盟各国 emphasizes each individual member country, often in a collective sense.
Compound of 加盟 (かめい, 'affiliation, membership') and 各国 (かっこく, 'each country, various countries').