What you need to know about the Catalan independence referendum Voters in the Spanish region head to the polls on Oct. 1.

 -- It is not often that a plebiscite is banned in a democracy but that is exactly what happened in the case of the upcoming Catalan independence referendum in Spain set to be held on Oct. 1.

The vote has not only been deemed unconstitutional but also illegal by the Spanish government, which has responded strongly to the independence movement. Government officials have taken control of Catalan finances and rescinded its autonomy.

Police have raided dozens of Catalan regional governments and detained 14 senior politicians over their support for the organization of the referendum. Police have also raided political parties' headquarters and seized material, including pamphlets and election materials. The government has threatened that anyone handling or supplying electoral material risks prosecution and has instructed the police to stop the vote from going ahead in the region.

In response, thousands in the independence movement are now planning to stage long-term street protests and thousands have demonstrated in Barcelona against the arrest of people associated with the independence vote, demanding their immediate release.

The vote is five days away and neither side looks like it is backing down.

Many are asking how could this apparently anti-democratic activity could happen in democratic Spain. Here's what you need to know:

What and where is Catalonia?

Catalonia, located in northeastern Spain, is a semi-autonomous region with its own local parliament. Catalans, as the locals call themselves, have been part of a distinct entity since the 11th century and have their own language and traditions.

Catalonia has been a part of Spain since the 15th century. Its language and culture have remained over the centuries despite the region's closer integration into the Spanish nation-state. The region was first given formal limited autonomy in the early 20th century. Catalan identity was brutally repressed under the fascist regime of Francisco Franco, who banned locals from speaking the regional language and giving children traditional Catalonian names. The pro-independence sentiment, however, remained strong in Catalonia.

After the death of Franco and the introduction of a democratic government, Catalonia's unique identity and culture has been formalized and flourishes in modern democratic Spain. There are regional elections for parliament with an executive and local government and Catalan is the official language by law. The region has become one of the most prosperous and important in the country, with the city of Barcelona, and its population of nearly 5 million people, at its heart.

According to the Public Diplomacy Council of Catalonia, it is the richest region in Spain, accounting for nearly 25 percent of Spanish exports. Just 16 percent of Spain's population lives in the region.

Why is there a referendum?

The political push for Catalan autonomy has existed since the 20th century and accelerated with the establishment of democracy in the 1970s, but a full-blown Catalan independence movement evolved after the fallout from the financial crisis of 2007 and 2008.

Local Catalan political parties began to actively agitate for independence on the back of a failing national economy and a sense that the region was paying more in taxes than it was getting back in benefits.

"Spain convinced Catalans to become independent. They created this situation," said Marc Gafarot, a political analyst at the Barcelona Center for International Affairs. "Catalonia was simply asking for a reduction of participation in a Spanish tax system that transferred money from the richest regions to the poorest. It was clearly targeting and exploiting the Catalonian region."

The pro-independence movement held an earlier symbolic vote in 2014 in which Catalonia voted for independence -- 2.25 million people voted (a turnout of just 37 percent) with 81 percent of the voters saying yes to independence.

The upcoming referendum is different, having been organized by the Catalan government and ratified by its parliament, which is dominated by Catalan separatist parties, lending it legitimacy. Spanish Prime Minister Mariano Rajoy said of the move, "Separatists invented a new legal order."

The question being put to Catalans is simple: “Do you want Catalonia to be an independent country in the form of a republic?”

What has been the Spanish government’s response?

The Spanish government is not waiting for the result of the referendum to respond. The Spanish Constitutional Court has suspended the vote, though Catalonia's pro-independence government says it will be maintained and is challenging the order.

The suspension was requested by Rajoy, who argued that the referendum is illegal under the country's 1978 constitution. The Spanish public prosecutor's office asked the Catalonia Police including Mossos (Special Forces), Guardia Civil (Local Police) and Cuerpo Nacional de Policia (National Civil Police Forces) to confiscate any voting material used to organize the "crime" of the illegal referendum, including ballot boxes, electoral propaganda flyers and printers.

"It's not just about independence. Spain is making itself a fool with the international community," Raul Romeva, Catalonia's minister of foreign affairs, told ABC News, adding that there are only two possible paths for Spain to take: "Democracy or repression."

Earlier this month, La Guardia Civil confiscated 10 million paper ballots and Spain has detained 14 Catalan officials including Josep Maria Jové, the secretary general of economic affairs. Potential polling locations in the region were additionally raided.

Gafarot predicted Spain's actions could have an unintended consequence: "Because of all this buzz, the pro-Catalonia independence vote will probably be stronger than ever."

What happens next?

The Catalan separatists have accused the Spanish government of being heavy-handed and mounting "a coup against democracy." They are adamant that the vote will go ahead, even if it has to be as a clandestine plebiscite.

An anonymous militant organizer confirmed to ABC News that 6,000 ballot boxes have been stored in a secret location for the coming referendum and ongoing street protests will be conducted as part of the campaign against what they see as interference by the Spanish government in their affairs.

"Spain now is showing his real face to the rest of the world," said the organizer. "I am young and [a] few years ago I would not have thought we had to fight for our rights. We are in Europe. It's a shame."

"Spain let us vote in 2014. This time they refuse because they know it's happening," he continued, adding, "I hope it's the last battle."