The Watermelon War was a riot that occurred on the morning of April 15, 1856, in Panama City in what was then the province of Panama in the Republic of New Granada, now the Capital City of the Republic of Panama.
Throughout the 19th century, U.S. involvement in the isthmus of Panama increased as it became the most convenient area in Central America for quick transoceanic transit. U.S. expansion westward accelerated after the Mexican–American War and the California Gold Rush and the United States felt a growing need for faster access to the Pacific during a time when the American mid-west and western regions were difficult to travel. This led to recurrent negotiations between the governments of the Republic of New Granada, of which Panama was a province, and the United States of America. The focus of these early negotiations was for rights and protections concerning the free passage of goods and people through the isthmus. The most important treaty resulting from these negotiations was the Mallarino-Bidlack treaty of 1846 which although in essence was concerned with free trade, included a clause in which the Republic of New Granada recognized that the United States could intervene to guarantee the neutrality of the isthmus. This clause, originally meant to protect against foreign control over the isthmus, was eventually interpreted to permit U.S interventions to protect American interests against any dangers resulting from local disturbances or the many civil wars that plagued New Granada (modern day Colombia). Until the construction of the Panama Canal, the main concern for the U.S on the isthmus was the protection of the Panama Railway which was built in the 1850s. The frequent transit of foreigners along the railway and the perpetual presence of U.S. ships in Panamanian ports became common and led to increased interaction between both local New Granadian Panamanians, and U.S. citizens.
On the morning of April 15, 1856, the U.S. steamer John L. Stephens transported about 1,000 passengers to Panama City. However, the station was located at the waterfront and Panama City did not then have any wharfs where ships could dock. Therefore, ships like John L. Stephens had to dock on a surrounding island, in this case Taboga Island, and then be ferried to Panama City. The passengers could only be ferried during high tide and, on this particular day, the John L. Stephens arrived during low tide; therefore, the passengers had to sit and wait on high tide.