This article addresses the domestic and international conditions that influence regional integration. The national political elite is assumed to be opportunistic and will opt for regional integration when the domestic and international conditions provide economic gains for their constituencies through greater economic integration. The hypotheses state that increases in regional integration in Latin America and the Caribbean (ANCOM, CACM/SICA, CARICOM, and MERCOSUR/MERCOSUL) occur during periods of relative power asymmetries among pairs of countries, when mutual trade interests are high, and when alliance portfolios are similar. We test the hypotheses using aggregate data of country dyads from 1960 to 1997. To measure regional integration, we use an index referred to as the Integration Achievement Score. OLS and Cox proportional hazards regression estimates largely support our claims.