Secession of Panama from Colombia
The secession of Panama from Colombia was formalized on 3 November 1903, with the establishment of the Republic of Panama and the abolition of the Colombia-Costa Rica border. From the independence of Panama from Spain in 1821, Panama had simultaneously declared independence from Spain and joined itself to the confederation of Gran Colombia through the Independence Act of Panama.
Source: Wikipedia — Secession of Panama from Colombia (CC BY-SA 4.0)