What was the name of a civil war fought in Colombia that began on 17 October 1899?

The Thousand Days' War (Spanish: Guerra de los Mil Días) was a civil war fought in Colombia from 17 October 1899 to 21 November 1902, at first between the Liberal Party and the government led by the National Party, and later – after the Conservative Party had ousted the National Party – between the liberals and the conservative government.

Caused by the longstanding ideological tug-of-war of federalism versus centralism between the liberals, conservatives, and nationalists of Colombia following the implementation of the Constitution of 1886 and the political process known as the Regeneración (es), tensions reached a fever pitch after the presidential election of 1898, and in 17 October 1899, official insurrection against the National government was announced by members of the Liberal Party in the Department of Santander. Hostilities didn't begin until the 11th of November, when liberal factions attempted to take over the city of Bucaramanga, giving way to active warfare.

It would end three years later with the signing of the Treaty of Neerlandia and the Treaty of Wisconsin. The war resulted in a Conservative victory, and ensured the continued dominance of the Conservative Party in Colombian politics for another 28 years. Colombia's political structure as a unitary state has not been challenged since.