With tensions high along the entire south-western coast of South America due to the Spanish blockade over the Chinca Islands dispute, Peru had sought and negotiated an alliance against Spain with Chile, agreed on December 5, 1865. The Chilean Congress ratified the agreement and, although there had been Peruvian-Spanish naval clashes for months previously, Peru officially declared war on Spain on January 14, 1866. (By John Osborne)
Source Citation
"Peru," The American Cyclopedia and Register of Important Events of the Year 1865 ... (New York: D. Appleton and Co., 1869), 699.