But they also affirmed that there would be no sovereignty but that of the Spanish nation.

Even before the Constitution was enshrined, Catalonia got back some of the autonomy it lost in the civil war of the 1930s, as part of a political deal brokered by politicians in Madrid to ensure that Catalans would embrace Spain’s political structure.

In fact, Adolfo Suárez, who became Spain’s conservative prime minister, restored the Generalitat, the regional government of Catalonia, as the only institution of the Spanish Second Republic of the 1930s to be reinstated after Franco’s dictatorship.

In 1981, Spain’s main parties agreed to divide the country into 19 regions, including two city enclaves in northern Africa, Ceuta and Melilla. By 1995, each region had drawn up its own statute of autonomy.

“The Constitution was seen as an instrument of transition and peace that in the first years could also create greater social linkage and economic development,” said Miguel Herrero de Miñón, one of the seven founding fathers of the 1978 Constitution.”

“Other concepts were then added later,” he added. “The most disastrous of them was to generalize the map of the regions.”

In October, Spain’s two main parties — Mr. Rajoy’s Popular Party and the Socialists — agreed to form a commission to prepare a constitutional reform. Their decision was in large part an attempt to defuse the Catalan crisis.

But the commission will take six months to prepare its preliminary report, and there is no guarantee that politicians will reach consensus over what to change, in particular when it comes to the sensitive issue of regional power.