Most Important Events In Spanish History By phoebegrace1234 1478 The Catholic Spanish Inquisition began 1898 Spain lost colonies including Cuba, Guam and Puerto Rico 1931 Spain Becomes A Republic 1968 West African colony of Spanish Guinea granted independence as Equatorial Guinea 1975 Juan Carlos de Borbon declared king. Spain became a constitutional monarchy 1977 Democratic elections held 1978 Spain's new constitution established a parliamentary monarchy 1982 Spain joined NATO 2002 All currency replaced by the Euro