All 35 independent nations of the Americas are member states of the Organization of American States (OAS). Upon foundation on 5 May 1948 there were 21 members:
The later expansion of the OAS included the newly independent nations of the Caribbean (most of whom gained independence only after World War II) and Canada. Members with later admission dates (sorted chronologically):
(1) On June 3, 2009, the Ministers of Foreign Affairs of the Americas adopted resolution AG/RES. 2438 (XXXIX-O/09), that resolves that the 1962 resolution, which excluded the Government of Cuba from its participation in the inter-American system, ceases to have effect in the Organization of American States (OAS). The 2009 resolution states that the participation of the Republic of Cuba in the OAS will be the result of a process of dialogue initiated at the request of the Government of Cuba, and in accordance with the practices, purposes, and principles of the OAS.
(2) On July 5, 2009, the Organization of American States (OAS) invoked Article 21 of the Inter-American Democratic Charter, suspending Honduras from active participation in the hemispheric body. The unanimous decision was adopted as a result of the June 28 coup d’état that expelled President José Manuel Zelaya from office. On June 1, 2011 members of the Organization of American States (OAS) lifted the suspension of Honduras’ participation in the organization.
http://www.oas.org/en/member_states/default.asp http://www.state.gov/secretary/rm/2011/06/164813.htm