Social and political movements have adopted flags, to increase their visibility and as a unifying symbol.
The socialist movement uses red flags to represent their cause. The anarchist movement has a variety of different flags, but the primary flag associated with them is the black flag. In the Spanish civil war, the anarchists used the red-and-black bisected flag. In the 20th century, the rainbow flag was adopted as a symbol of the LGBT social movements. Its derivatives include the Bisexual pride and transgender pride flags.
Some of these political flags have become national flags, such as the red flag of the Soviet Union and national socialist banners for Nazi Germany. The present Flag of Portugal is based on what had been the political flag of the Portuguese Republican Party previous to the 5 October 1910 revolution which brought this party to power.
The Rainbow flag of the LGBTsocial movement. Similar flags are used in Europe to support pacifism and in Peru and Bolivia to represent the indigenous peoples of the Andes.