When the Ten Years' War erupted in October 1868, Zambrana threw his support behind the insurrection against Spanish authority.

[6] On April 11, the Assembly set up the government with Salvador Cisneros Betancourt as president and Zambrana and Agramonte as secretaries.

[7] In Havana, on November 7, 1870, a court-martial found Zambrana and other members of the Cuban Junta of New York guilty of treason and rebellion, with a death sentence by garrote pending if they were captured by Spanish authorities.

[10] Following extensive preparations and fundraising, Zambrana and Gen. Manuel de Quesada traveled to Latin American countries including Panama, Venezuela, Colombia, and Peru.

Zambrana was appointed as Envoy Extraordinary and Minister Plenipotentiary by Próspero Fernández Oreamuno, President of the Republic of Costa Rica.