Why did Panama separate from Colombia in 1903?

The separation of Panama from Colombia in 1903 was primarily driven by the rejection of the Hay-Herrán Treaty by the Colombian senate. This treaty would have granted the United States rights to build and control a canal across the isthmus.123

Following this rejection, a group of Panamanian revolutionaries—already frustrated by the Colombian government’s property requisitions and the impressment of men during the War of a Thousand Days—sought independence. With the encouragement and strategic support of the United States, which sought to secure the canal project, the revolutionaries proclaimed independence on November 3, 1903.134

The U.S. government facilitated the secession by preventing Colombian forces from suppressing the rebellion, notably by using the U.S.-administered railroad to block troop movements. Shortly after, the new Republic of Panama signed the Hay–Bunau-Varilla Treaty, granting the United States exclusive control over the Canal Zone. This event significantly embittered diplomatic relations between Colombia and the United States for many years.123