The conviction of nine Catalonian leaders on charges of sedition for their roles in organising the 2017 illegal referendum on separation by the Spanish Supreme Court has made hundreds of thousand people, many of them with the Catalonian independence flag draped over their backs, protest in the streets of Barcelona since Monday last.

The leaders were sentenced to prison terms of between nine and 13 years. The longest sentence was reserved for former Catalonian Vice President Oriol Junqueras. Three other leaders were cleared of sedition charges, but convicted of misappropriating public funds.

The court order was rejected by the separatist Catalonian government led by President Quim Torra and has spurred its independence struggle.

This is Spain’s biggest political crisis since democracy was restored in 1975, after the death of military dictator Gen Francisco Franco.

Torra described the Supreme Court order as unjust and undemocratic and called for mass civil disobedience, leading the authorities in Madrid to send thousands of national policemen to supplement the Catalonian regional police.

Protesters have attempted to shut down Barcelona’s airport, causing long delays and flight cancellations.

Political turmoil in Spain has been endemic. The country recently faced a fourth national election in as many years due to the inability of the main political parties to form a stable government.

The dysfunction in Madrid has been made worse by a rising independence movement in Catalonia, one of Spain’s wealthiest and most productive regions with a distinct history dating back more than nine centuries. Alfred Bosch, foreign minister of Catalonia, has accused successive governments in Madrid of escalating the crisis by refusing to allow a legal referendum on Catalonia’s future.

The hard line taken by the central government has propelled support for the independence movement. When Franco died, the region was granted autonomy under the 1978 Constitution and Catalonia prospered as part of the new democratic Spain.

Acting Prime Minister Pedro Sanchez’s Socialist Party government has advocated dialogue with Catalonian leaders, but refused a constitutional referendum. Except for the Podemos Party, all of Sanchez’s national rivals consider the issue of Catalonia’s status within Spain non-negotiable. He is under pressure to initiate extradition proceedings against former Catalonian President Carles Puigdemont, who remains in self-imposed exile in Belgium to avoid prosecution in Spain.

Catalonia has a population of 7.5 million and accounts for almost 20 per cent of Spain’s GDP. It has been a part of Spain since the 15th century. Generations of people from the poorer parts of Spain have moved to Catalonia for work, forming strong family bonds with other regions. Madrid’s refusal to recognise Catalonia’s right to self-determination has left it with a black eye in diplomatic circles. The European Union, seized of the Brexit countdown, has treated the crisis as an internal matter of Spain, deaf to the Catalonian separatists’ pleas for support.