Panama is located in Central America, bordering both the Caribbean Sea and the North Pacific Ocean. Panama became a Spanish colony in the early 16th century, breaking with Spain in 1821 and entering the Republic of Greater Colombia. Seceding from Colombia, Panama became independent in 1903 and promptly signed a treaty with the United States, allowing for the construction of a canal and U.S. sovereignty over the Panama Canal Zone. The United States completed the canal in 1914, and the canal has since been Panama's economic base. From 1903 until 1968, Panama was a constitutional democracy dominated by a commercially-oriented oligarchy. A coup in 1968 resulted in the establishment of the military government, and the movement to end American control of the Canal Zone gained momentum. In 1977, an agreement was signed for the complete transfer of the Canal from the U.S. to Panama by the end of the century. With U.S. help, the dictatorship under General Manuel Noriega was ended in 1989. The Panama Canal was transferred to Panama by the end of 1999, ending nearly a century of American jurisdiction over one of the world's most strategic waterways. In 2006 Panamanians approved an ambitious plan to expand the Canal to allow it to handle more and larger vessels. The project began in 2007 and is expected to be completed in 2014-15.