In 1869, Grant commissioned his private secretary Orville E. Babcock and Rufus Ingalls to negotiate the treaty of annexation with Dominican president Buenaventura Báez.

Grant had authorized the U.S. Navy to protect the Dominican Republic from invasion by neighboring Haiti while the treaty annexation process took place in the U.S. Senate.

A treaty was drafted by Secretary of State Hamilton Fish that included the annexation of the country itself and the purchase of Samaná Bay for two million American dollars.

When debated in the Senate, Sumner staunchly opposed the treaty, believing the annexation process was corrupt and that the Dominican Republic was politically unstable, having a history of revolution.

Sumner believed that Báez was a corrupt despot and that the use of the U.S. Navy by Grant during the treaty negotiation to protect Santo Domingo was illegal.

In 1867, during President Andrew Johnson's administration, the Dominican government, under threat of Haitian invasion, had asked to be annexed by the United States.

[4] Fabens, along with his Texan business partner William L. Cazneau, had personal interest in securing U.S. annexation as, under the Báez government, they stood to own one tenth of the Dominican Republic's land.

Fish appointed Benjamin P. Hunt with diplomatic authority to look into the Dominican Republic's debt and whether the people actually desired to join the United States.

[6] Fearing European powers might take control of Santo Domingo, Grant also mentioned the need to maintain the Monroe Doctrine.

[7] He used the excuse of European interest in the island to advocate annexation as a means to defend the U.S., preventing a rival power from gaining a foothold in the Western Hemisphere.

In addition to the coaling station, Grant felt that the Dominican Republic's immense resources could provide sustenance for the mass emigration of African Americans from the South of the U.S. to Santo Domingo.

Their mass movement to Santo Domingo would have made African Americans “master of the situation, by enabling them to demand [their] rights at home on pain of finding them elsewhere.”[9]

Sumner opposed the treaty believing annexation would be expensive, launch an American empire in the Caribbean, and would diminish independent Hispanic and African creole republics in the Western Hemisphere.

[23] Grant was able to get Congress to allow an investigation commission to be sent and make an objective assessment as to whether annexation would be beneficial to both the United States and the Dominican Republic.