This research proposes, as a general objective, to analyze the relations between the Federal Government and the federated entities in the formation of the Brazilian foreign policy for the Amazonian question. To this end, it is developed a quantitative and qualitative study of the investments made by the Inter-American Development Bank (IDB) in subnational entities in the Legal Amazon within the context of the policies of Federative Diplomacy and International Federative Cooperation of Brazilian foreign policy. Thus, the article has as a central problem if the subnational dimension of the federated entities of the Legal Amazon was strengthened through the IDB's investments in the region in environmental issues. The methodological aspects are traced from the approach of institutional analysis of subnational engagement policies. In addition, the analysis of the IDB's investments is carried out by primary sources, in addition to a bibliographic review on two debates on Foreign Policy Analysis (FPA), the pluralization of actors, and the character of public policies on foreign policy. In summary, the results of the research point to the central role of the Federal Government's federal relations policies in strengthening the states of the Legal Amazon in their international actions and the search for investments.