In the context of the international economic crisis (1929 crash), the dictatorship of Primo de Rivera faltered, presenting his resignation to the king on January 28, 1930. On 12 April 1931 held elections that brought an end to the monarchy. In Barcelona, he won overwhelmingly nationalist party Esquerra Republicana de Catalunya, with a total of 25 council members. On 14 April, President of the Generalitat reinstated, Francesc Macia, proclaimed the Catalan Republic as part of the Iberian Federation. Also, the September 9, 1932 approved the Statute of Autonomy of Catalonia. The first years of the Second Republic meant a profound social transformation, sign laws adopted many progressive conditions improved lower classes. However, the triumph of right in the 1933 elections marked a further decline in social development. After several disputes with the central government, President Lluís Companys proclaimed October 6, 1934 the Estat Català, ruling that was quickly crushed by the army. Staff was discontinued, and the regional government passed directly into the hands of central government. However, the change of government with the Popular Front victory in the elections of February 16, 1936 entailed the restoration of the Generalitat and the president Companys.
In the summer of 1936 Barcelona is preparing to organize another international event: the People's Olympics. To this end, the Olympic Stadium was renovated and fitted out the mountain of Montjuic. However, although everything was ready, the Games could be held, because in July the military began its military coup against the Second Republic, giving rise to the Civil War. On July 19 several military columns approached the center of the city with the intention of taking the most strategic points to gain control of the population. However, the firm organized resistance by the troops of the Government, civil guard, who remained faithful to the Republic, and the urban militias, led to the failure of the uprising in the city. General Goded, who had flown in from Mallorca to take over the rebel government in Catalonia, was arrested and later fusilado.36
In Barcelona underwent a revolutionary process by which many of the companies and services were collectivized by unions such as the CNT and the UGT. The authority of the Government of the Republic and the Government was theoretical, effectively controlling the streets by anarchists. However, since the events of May 1937, which confronted the pro-Soviet communist-party PSUC first win the war with the anarchists and communists Trotskyist POUM trend advocates do first social revolution, the influence of the anarchists decreased. This small civil war in the largest state left a toll of 200 dead, including the POUM leader Andreu Nin.

George Orwell, Barcelona said on those days in Homage to Catalonia:

For the first time in my life, I was in a city where the working class took the reins. Almost all buildings, regardless of their size, were in the hands of workers and covered with red flags or the red and black flag of anarchists, the walls held the hammer and sickle and the initials of the revolutionary parties, almost All the temples had been destroyed and their images, burned. Everywhere, gangs of workers engaged systematically demolished churches. In every coffee shop and all were signs proclaiming their new condition of socialized services, even the shoeshine boys had been collectivized and their boxes were painted red and black. Waiters and dependent looked to the client face to face and was treated as an equal. The servile and even ceremonial forms of the language had disappeared. Nobody said sir, or gift, nor you, everyone is trying to "comrade" and "you" and said health! instead of good morning.
                                                                                                                                                                                    George Orwell, Homage to Catalonia.

During the war, Barcelona was bombed several times by the army coup, the first big capital was bombed by modern aviation. The first bombing was the Italian cruiser Eugenio di Savoia on 13 February 1937 that left 18 dead. The first air raid took place on 29 May (60 dead), the numerous aftershocks that occurred throughout the contest (with special virulence from 1 to January 30, 1938). The final balance was approximately 2,500 victims, mostly civilians.
The city was occupied by the partisan army on 26 January 1939, which abolished the autonomous region of Catalonia and its political institutions, such as the Generalitat, and banned the Catalan language and its cultural manifestations. Barcelona plunged during the nearly forty years of Franco's dictatorship, in a great social and cultural decadence.