Spain’s prime minister, Mariano Rajoy, often refers to his country as “the oldest nation in Europe.” That view is based on the 15th-century political union that resulted from the wedding of Isabella of Castile and Ferdinand II, the monarch of Aragón, whose kingdom included Catalonia.

Catalans commemorate as their national day a 1714 defeat at the end of the War of the Spanish Succession, when Barcelona was captured by the troops of Philip V, the first Bourbon monarch of Spain. Philip cracked down on Catalans and destroyed part of Barcelona.

“Later on, nation-building initiatives in Spain have been designed and implemented not only to keep the country together as one nation, but also to consolidate a hierarchical system of government thought to ensure that both Madrid and Castilian language and cultural values would play a prominent and almost exclusive role in shaping the country,” said Elisa Martí-López, a history professor at Northwestern University.

How has Spain’s modern Constitution enshrined the idea of autonomy?

When a new Constitution came into force in 1978, three years after the death of the dictator Gen. Francisco Franco, its framers sought to recognize the portions of the country with distinct cultural heritage.

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.