Catalonia's regional government, led by then-President Carles Puigdemont, declared independence in late October last year. The announcement followed a controversial referendum in which 90 percent of the 43 percent of potential Catalan voters who took part voted in favor of independence.
The announcement led to Spain's invoking Article 155 and seize control of the region. It marked the first time since the fall of dictator Francisco Franco in 1975 that the central government has taken direct control of one of Spain's 17 semi-autonomous regions. Puigdemont, who was charged with "rebellion" and "sedition," took exile in Belgium.
The basic guide to Catalonia and the Catalans
Located in the northeast of the Iberian peninsula, Catalonia has been a part of Spain since the 15th century.
Catalan separatists stress the fact that Catalonia is a nation with a distinct language, culture and history. Independence, they say, will protect the Catalan nation from the encroachment of Spanish language and culture.
The Catalan language developed independently of Spanish, deriving from the Latin spoken by Romans who colonized the area in the 2nd century BC. The Roman occupation harmonized the various cultures in the region into one.
Following the Muslim conquest of the Iberian peninsula in the 8th century, the inhabitants of the region turned to the Frankish leader Charlemagne for help. The province of the Spanish March was born, acting as a buffer between Muslim Hispania and Christian France.
The Muslim Moors took Barcelona again in 985 and, having received no support from the Franks this time, an independent state was proclaimed, taking the name Catalonia.
Catalonia emerged from the conflicts in Muslim Spain as a regional power, as Christian rulers entrenched themselves in the region. Catalonia became part of Spain in the 15th century when there was no successor to the throne.
There then followed periods of great instability, when Catalonia was under French protection after revolting against Spanish rule in the Franco-Spanish war. During the war of Spanish succession, Catalonia found itself alone and eventually fell to Spanish forces in 1714.
For centuries that followed, Catalan rights and the language were banned, universities closed and the Catalan nation was lost.
Its revival was helped by the Industrial Revolution.
An economic powerhouse
Catalan products were highly sought after in Spain in the 18th and 19th century, and the region grew rich on the back of trade with the Americas. Barcelona was known as the "Manchester of the Mediterranean."
Today, it is one of the wealthiest regions in Spain, Catalonia is still home to much of Spain's manufacturing and financial sector and makes up one-fifth of the country's GDP.
The region has long complained that its financial prowess subsidizes poorer areas, saying it sends €10 billion ($12 billion) more to Madrid than it receives back.
The 2010 Supreme Court decision restricting the region's control over finances fueled resentment at a time when the country was struggling in the aftermath of the 2008 financial crisis.
Opponents of the financial argument point out that it is only fair that Catalonia helps support less-developed regions, considering that the constitution grants "self-government of the nationalities and regions and solidarity among them all."
The history of the independence movement
Catalan nationalists have pressed for greater autonomy for decades.
Former Spanish dictator Francisco Franco suppressed Catalan autonomy and identity during his 1938-75 rule. But the democratic constitution that emerged from dictatorship granted Catalonia autonomy in 1979.
Nationalist sentiment was sparked after the Spanish Supreme Court in 2010 overturned parts of a new 2006 Statute of Autonomy, which had been agreed to by the Catalan parliament and Spanish government with the support of a referendum.
Among the 14 articles in the Statute of Autonomy struck down by the Supreme Court were those that gave preference to the Catalan language and empowered the region's control over finances. Its ruling that there was no legal basis to describe the Catalan people as a "nation" enraged nationalists.
Massive Catalan nationalist protests ensued, leading to a non-binding referendum in 2014 despite Madrid calling it illegal. The referendum passed with 80 percent voting in favor, but turnout was less than 40 percent.
The referendum galvanized nationalists, who took control of parliament in 2015 following elections vowing to hold an official independence referendum.