In 1525, Pedro de Alvarado conquered El Salvador for Spain. In 1821, El Salvador declared independence from Spain and joined a federation of Central American states until 1838. From 1931 to 1979, El Salvador was ruled by a series of military dictatorships. In 1969, tensions between El Salvador and Honduras erupted into a brief war known as the "Football War" that started during a soccer game between the two countries.