• Este é um artigo publicado em acesso aberto e distribuído sob os termos da Licença de Atribuição Creative Commons, que permite uso irrestrito, distribuição e reprodução em qualquer meio, desde que o autor e a fonte originais sejam creditados.http://www.scielo.br/rbpi Revista Brasileira de Política Internacional ISSN 1983-3121 UNASUR, Brazil, and the South American defence cooperation: A decade later DOI: https://dx.doi.org/10.1590/0034-7329201700212 Rev. Bras. Polít. Int., 60(2): e012, 2017 Abstract UNASUR and its Defence Council (SADC) were created under a promising scenario of regional cooperation. Almost ten years later, a growing demand for regional cooperation arises, facing, however, low levels of political willingness from local governments. Through the lenses of structural and neoclassical realism, this paper suggests that the lack of support by governments, especially the Brazilian one, due to a change in how domestic ideas are developed, and a transformation in the regional balance of power, have contributed to these institutions' quick obsolescence. Introduction S outh America has experienced significant political changes since 2015, with changes in government having taken place in Argentina, Brazil, and Peru. In the near future, Chile, Colombia, Ecuador, and Bolivia will also undergo presidential elections while the prospects of the Chavismo in Venezuela tend to become even more critical as governance is under severe stress. A new political environment is gradually emerging on the subcontinent, directly challenging most of the underpinnings of the regional political and institutional framework set up in the previous decade to embrace and foster security and defence initiatives at the regional level.Since its inception, the South American Union of Nations (UNASUR) has been the most important institutional framework for political dialogue on security matters on the subcontinent, in accordance with its vocation and with the mandate envisaged in the 2008 Brasília Treaty. Even though the need for a genuine South American institutional framework for such a dialogue had been widely recognized, and the creation of the South American Defence Council (SADC) hailed as a major step towards regional cooperation in security and defence matters, the fact that the SADC embraced consensus as a primary criterion for decision-making, while at the same time lacking binding decision-making powers, was perceived as a significant potential constraint if regional stability was to be severely undermined and regional action was deemed an imperative. If, on the one hand, those choices reflect a pragmatic assessment of the political conditions that should be acknowledged and met to allow the very existence of the SADC, on the other, they also imply severe restrictions on its entitlements to act, which confirms its vocation as a dialogue forum rather than as a decision-making and operative body.Even if a positive performance of the SADC during its first four/five years might be alleged, the changes in the political land...