ThePact of Ostend was an agreement signed on 16 August 1866 inOstend, Belgium, uniting the exiled SpanishProgressive Party,Democratic Party, and later theLiberal Union to overthrow the monarchy ofIsabella II of Spain, whose authoritarian rule had fueled political unrest. Spearheaded by GeneralJuan Prim, the pact aimed to dismantle the existing regime and establish a constituent assembly elected by universal suffrage, paving the way for theGlorious Revolution of 1868, which deposed Isabella II and initiated the democratic reforms of theSexenio Democrático (1868–1874).
By 1866, Spain faced mounting opposition toIsabella II’s monarchy, plagued by political instability and authoritarianism. In June, theSan Gil Barracks uprising [es], led by sergeants at Madrid’s San Gil artillery barracks, sought to topple her regime but was crushed by GeneralLeopoldo O'Donnell’sLiberal Union government, resulting in 66 executions.[1] In July, deeming O’Donnell too lenient, Isabella dismissed him and appointed GeneralRamón María Narváez of theModerate Party, who enforced harsh repressive measures, dismantling the Liberal Union’s power-sharing arrangement.
O’Donnell responded with a strategy he termedvacío en Palacio (“vacuum at the Palace”), withdrawing Liberal Union senators from the Senate to weaken Narváez’s legitimacy.[2] Yet, lingering resentment over the San Gil uprising prevented cooperation withJuan Prim’sProgressive Party. After O’Donnell’s death in November 1867, GeneralFrancisco Serrano assumed leadership of the Liberal Union, aligning it with the Pact of Ostend, signed a year earlier by the Progressives andDemocratic Party.[2]
Signed on 16 August 1866 inOstend, Belgium, the Pact of Ostend united the exiledProgressive Party andDemocratic Party under GeneralJuan Prim to overthrowIsabella II’s regime.[2] Its key objectives were:
The pact’s broad wording enabled later alliances, notably with theLiberal Union under GeneralFrancisco Serrano in March 1868.[2] HistorianJosep Fontana argues Serrano joined due to personal grievances—his arrest for petitioning to reopen the Cortes—and economic motives, as president ofFerrocarriles del Norte, seeking government aid for the struggling railway company.[3]
An action committee, led by Prim alongside figures likeCristino Martos andSalustiano de Olózaga, coordinated efforts.[2] Other key participants included military leaders likeBlas Pierrad [es] andManuel Pavía y Rodríguez de Alburquerque, and politicians such asPráxedes Mateo Sagasta andManuel Ruiz Zorrilla.[4]
Narváez countered with intensified repression. The Cortes, closed in July 1866, remained dissolved, and rigged elections in early 1867 secured a Moderate Party majority, reducing the Liberal Union to four seats.[5] In June 1867, new regulations abolished thevote of no confidence and absolved the government of accountability for actions during the closure, prompting an opposition deputy to call it a “coup d’état.”[6]
The Pact of Ostend laid the groundwork for theGlorious Revolution of September 1868, which oustedIsabella II, forcing her into exile inFrance.[2] Initiated by AdmiralJuan Bautista Topete and joined byJuan Prim andFrancisco Serrano, the uprising fulfilled the pact’s aim of dismantling the monarchy, ushering in theSexenio Democrático (1868–1874), a period of liberal reforms.
The Sexenio unfolded in three phases:
The pact’s emphasis on national sovereignty and democratic principles shaped these reforms, though internal divisions limited their longevity.[7]