During the first 30 years of the 20th century, Catalan industry went through a period of diversification, characterised by the spread of electricity and oil products. The labour movement consolidated its position with the founding of the CNT (1910) and achieved an eight-hour working day (1919). In the 1920s, the first great wave of immigration from the south-east of Spain began.

The political map began to be dominated by the Regionalist League and republican parties in 1901. The Mancomunitat de Catalunya (1914-1925), with Enric Prat de la Riba as its president, was a federation of the provincial councils. The declaration of the Second Republic in 1931 paved the way for the establishment of the Generalitat, with Francesc Macià and then Lluís Companys, from ERC (Republican Left of Catalonia), as its presidents. The military coup d'état of July 1936 was the start of a cruel civil war lasting three years. Franco's victory in 1939 signalled the beginning of a long dictatorship and the abolition of self-government.