The proposed annexation of Santo Domingo was an attempted treaty during the later Reconstruction era, with precedents under earlier administrations, but re-initiated by United States President Ulysses S. Grant in 1869, to annex Santo Domingo (as the Dominican Republic was commonly known) as a United States territory, with the promise of eventual statehood. President Grant feared some European power would take the island country in violation of the Monroe Doctrine. He privately thought annexation would be a safety valve for African Americans who were suffering persecution in the US, but did not include this in his official messages. Grant also believed that the acquisition of Santo Domingo would help bring about the end of slavery in Cuba and elsewhere. The proposal to annex Santo Domingo aligned with a broader US foreign policy strategy in the Reconstruction era, including pursuit of new markets in the Caribbean to absorb the increasing industrial output of American businesses. The island's raw material wealth made it an attractive prospect for the U.S. commercial interest of seeking economic expansion in the region.

In 1869, Grant commissioned his private secretary Orville E. Babcock and Rufus Ingalls to negotiate the treaty of annexation with Dominican president Buenaventura Báez. 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. Also included and supported by Grant was the provision that the Dominican Republic could apply for statehood.

The annexation process drew controversy: opponents Senator Charles Sumner and Senator Carl Schurz denounced the treaty vehemently, alleging it was made only to enrich private American and island interests and to politically protect Báez. Sumner believed that Baez was a corrupt despot and that the use of the US Navy by Grant during the treaty negotiation to protect the Dominican Republic from invasion by neighboring Haiti while the annexation process took place, was illegal. Sumner claimed that annexationists wanted the whole island and would absorb the independent black nation of Haiti. He, along with Schurz, also opposed mixed-race people becoming US citizens. Both men used arguments linking climate and race, stating that to annex the tropical area of Santo Domingo would be damaging to the Anglo-Saxons of the US, who were more suited to temperate climates, and to the black people of Santo Domingo, who they believed were more suited to tropical climates. A plebiscite ordered by Báez, who believed the Dominican Republic had better odds of survival as a US protectorate and could sell a much wider range of goods to the US than could be sold in European markets, registered an improbably low 11 votes against annexation, compared to over ten thousand for annexation. The country's unstable history was one of invasion, colonization, and civil strife.

The treaty ultimately failed to reach the two-thirds vote needed under the Treaty Clause (the vote was a tie). In order to vindicate the failed treaty annexation, Grant sent a committee, authorized by the United States Congress and including African American abolitionist Frederick Douglass, that investigated and produced a report favorable to annexation of the Dominican Republic into the United States. However, the annexation treaty ultimately failed because there was little support for it outside Grant's circle. The defeat of the treaty in the Senate directly contributed to the division of the Republican party into two opposing factions during the presidential election of 1872: the Radical Republicans (composed of Grant and his loyalists) and the Liberal Republicans (composed of Schurz, Sumner, Horace Greeley as presidential candidate, and other opponents of Grant).

Conflict and strife in Santo Domingo When the annexation was proposed, Santo Domingo had experienced decades of political instability, marked by civil wars, coups, and foreign occupations. Dominicans suffered under Haitian rule, which repressed their Dominican culture and Spanish language in favor of French. Following their achievement of independence in 1844, they experienced periods of both Republican and Authoritarian rule, characterized by political elites like Buenaventura Báez (who favored US annexation) and Pedro Santana (who favored Spanish annexation). In 1861, the country was occupied by Spanish forces, sparking a brutal guerrilla war for independence known as the Restoration War, which devastated the nation's economy and society.

The post-restoration period saw ongoing power struggles between Báez and his political opponents. Baez repeatedly sought US annexation to secure his grip on power, whilst also stabilizing the economy and gaining protection from Haiti. He presented the country's instability as a justification for foreign intervention, which critics viewed as prioritizing his own political power over national sovereignty.

Annexation proposal

Threatened by Haitian invasion, the Dominican government had asked to be annexed to the United States during President Andrew Johnson's administration in 1867. However, refusal by Congress meant that this did not make any progress.See , p. 449. As well as facing the threat from Haiti, which had been present since the invasion of Toussaint Louverture in 1801, there was the threat of internal revolt due to the tumultuous politics of Santo Domingo. There were a small group of American settlers on Santo Domingo, including William Cazneau and Joseph Fabens, who had arrived in the 1850s and, after pursuing the wealth of the island, owned one-tenth of the land in the Dominican Republic. They became involved in Dominican politics, and by the time Grant was in power self-interest caused fear of the impacts that volatile internal politics could have on their wealth. With these motives they supported the idea of annexing Santo Domingo to the US, and managed to gain the support of President Baez. However despite Baez’s attempts to sell Samaná bay and peninsula to the US in 1868, it was only when Grant was in power that Fabens managed to secure presidential support for the proposal of wider annexation.

Grant initially rejected ideas of expansion, but Fabens managed to persuade him of the benefits of annexation. This may have been because Grant believed that a separate annexation project in the Caribbean would have more success than previous attempts by his predecessors to annex the territory of Saint Thomas and that he had a greater chance of success due to the control his party had over Congress and the Committee of Foreign Affairs in both houses.

In 1869, Grant sent his aide General Orville Babcock to gather information on the Dominican Republic. Babcock was specifically requested to investigate the agricultural and mineral wealth of the island and the attitude of the government towards the US. Furthermore, current Secretary of State Hamilton Fish had fears over the race of the Dominican Republic and asked Babcock to collect information on the different races that lived there. Rather than official diplomatic authority, Grant personally gave Babcock special agent status with an introduction letter for the Dominican president.

Grant feared that other European powers would take control of Santo Domingo and used the need to maintain the Monroe Doctrine as one of his reasons behind annexation. Grant's vision aligned with the doctrine and its aim to protect US interests from that of Europe in the western hemisphere, and by using its language he justified expansion. However it went further than this in that, whilst earlier iterations of the doctrine (which was established in 1823) sought to remove European influence so the US could sustain their presence in a slave based economy, Grant aimed to use the annexation as part of his larger goal to expand liberty and freedom throughout the hemisphere.

Racial aspect to the argument

The annexation proposal was both reinforced and hindered by white nationalist ideas. In the post-Civil War US, the American notion of manifest destiny had evolved to encompass territory outside of continental America. There were many white Americans and US senators who feared incorporating a racially mixed population into the US, largely due to its capacity to dilute the white vote and reshape the status quo, as well as associating the prospective new population with moral decline.

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 US to Santo Domingo. He hoped that this exodus would benefit America, Santo Domingo, and the African Americans since it would lower the chances of a race war within the US; provide skilled workers to the island; and enable the 4 million newly emancipated African Americans in the southern US to leave the racism and poverty of the post-war South and start their own republican nation under the guidance of the US. In his final annual address to the nation in 1876, Grant said that the annexation would have raised the material and political fortunes of millions of African Americans. 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.”

Grant also felt that if the US used its resources and technology to turn Santo Domingo into a huge producer of tropical goods (like tobacco and sugar) then it would reduce America's reliance on trade with slave states like Brazil and Cuba, thus helping to end slavery in the Americas.

Although Grant framed the proposal as a moral effort to protect Dominicans, reinforce the Monroe Doctrine, and provide a haven for African Americans fleeing persecution in the Reconstruction South, this rhetoric has been debated by historians as masking deeper concerns of racial integration and white supremacy. Grant's list outlining his reasons behind annexation, 'Reasons Why Santo Domingo Should be Annexed to the United States?', argued:

'The colored man cannot be spared until his place is supplied, but with a refuge like Santo Domingo his worth here would soon be discovered and he would soon receive such recognition as to induce him to stay: or if Providence designed that the two races should not live together he would find a home in the Antillas'

The safety valve of African American emigration that Grant's writing describes potentially indicates that annexation was influenced by an evolved manifest destiny, that justified American expansionism as a civilizing mission to export Anglo-American values to underdeveloped nations incapable of self-governance. However Nicholas Guyatt argues that the annexation process should be seen in a more complex context rather than a racist plan more similar to the earlier efforts of the American Colonization Society. The annexation of Santo Domingo was discussed where it would be incorporated into the US as a state of the Union and supporters of annexation believed that this would come with significant white migration to the Caribbean, rather than it being a way of removing the African American population.

Abolitionists and annexation The prospect of annexing Santo Domingo was discussed not only among Grant and official policy makers, but also among non-state actors such as abolitionists. Within the context of Reconstruction and recent post-Civil War emancipation, annexation on equal terms to the states of the US and the promise of gaining one hundred and fifty thousand new black citizens, was seen as having great potential.