The extent to which a region will deepen its economic integration and adopt the characteristics of a supranational state is partially influenced by the factors prompting states to start the regionalization process. Four broad reasons for pursuing economic integration can be identified.

Reactive regionalism is also referred to as defensive regionalism, suggesting that states choose to pursue economic integration to protect their shared interests from a specific or nebulous external threat. In a historical context, reactive regionalism was viewed by developing countries as a technique for providing the large internal markets needed to support nascent industrial sectors. Although the decline of import-substitution industrialization strategies and the rise of neoliberalism have greatly reduced the protectionist aspect of reactive regionalism, the idea of providing a common level of shelter for internal producers does remain in integration projects such as the South American trade bloc Mercosur.

The more common motive for contemporary economic integration projects lies in the logic of defensive regionalism. Here the participating states are reacting to perceived threats in the international economic environment. In some instances, such as Canadian participation in the North American Free Trade Agreement (NAFTA), the regional economic integration route was pursued to prevent a country from becoming isolated in a global economic system that appeared to be increasingly drifting toward a series of large economic blocs. Other regional groupings, such as the Andean Community and Mercosur, emerged partly as an attempt to use the expanded internal market as a lure to attract foreign direct investment (FDI) in an increasingly competitive international investment climate. Either way, the common element is that the participating states are seeking to use their combined economic mass and density to protect shared interests and to mitigate external vulnerabilities.

The most prevalent example of an economic integration emerging as part of an effort to ensure peace and security is the European Union (EU). As the neofunctionalist school suggests, the idea is to increase economic interpenetration between erstwhile hostile countries, seeking to raise the level of interdependence to the point where armed conflict and sustained mutual isolation become economically unsupportable. This underlying rationale can either emerge as a consensus position between participating states, as was partly the case in Argentine-Brazilian approximation in the 1980s and the formation of the South Asian Association for Regional Cooperation (SAARC), or be suggested as a solution to simmering hostilities by mediating actors as an effective method for diffusing potential conflicts, as has sometimes been the case with the South American infrastructure integration program launched in 2000.

The defensive character of many integration projects is in some cases eclipsed by a desire to reduce transaction costs within a regional space that is seeing growth in transnational production structures. Here the example of the Association of Southeast Asian Nations (ASEAN) is instructive, with a sustained rise in the regional distribution of production structures creating pressure for increased logistical and regulatory cooperation to facilitate the exchange of production factors. Significantly, an efficiency-seeking rationale to economic integration will not necessarily bring about pressure for labour mobility and often completely rejects the sorts of political approximations implicit in the deeper forms of economic integration. The profit-making potential of economic cooperation within the region remains the dominant factor, with only tangential attention being given to notions of social or political integration.

Although rarely explicitly framed as the need to externalize the rationale for politically contentious policies, economic integration has emerged as a device used on the domestic political stage. In South America the pursuit of an economic integration project was one justification used by pro-democracy factions in Argentina and Brazil in the late 1980s to neutralize lingering calls for a return to authoritarianism. Democratic governments in developing countries have also used the need to adhere to regional commitments as the justification for the pursuit and implementation of the Washington Consensus model of neoliberalism. Particularly important in this respect has been the reduction of state supports for local industries, the lowering of high tariff walls, and the privatization of state-owned firms. The pattern is thus one of domestic governments placing the blame for some of the politically difficult neoliberal economic programs pursued in the 1990s on the need to meet the country’s regional commitments, with the integration project being presented as the source of long-term and sustainable economic advantages as well as a collectively improved insertion into the international economy.