The War of the Pacific (1879-1884) which pitted Peru and Bolivia against Chile, represents an armed conflict marked by the realism policies that impose national interest, from other States, altering the regional political balance, under the justification of territorial claims. This policy affected not only the belligerents, but also other countries that could join the confrontation, seeking to change their status quo. Ecuador represents this consideration, in that its participation could strengthen its south border with Peru, pending since emancipation. Was the internal political weakness that did not allow to specify a possible intervention? This historical process, from the perspective of classical realism in international relations, where a country's domestic scene, is a determinant factor in the projection of its foreign policy will be studied in the following pages.