There is no official start date to the Catalonian independence movement, but one thing is for sure, Catalonia has persevered through years of being apart of a country they clearly do not want to be.
In 2008 the separatism became more deeply rooted because of the economic crash and Spanish spending cuts. The Catalan people believe that Catalonia sends too much money to other parts of Spain (because taxes are controlled by the government in Madrid.)
After years of the pro-independence movement, there was a referendum on October 1st, 2017, which was declared illegal by the Spanish Constitutional Court, and despite almost 90% of Catalan voters being pro-independence, there was only a 43% turnout.
Then, on the 27th of October, the separatists which ruled the parliament in Catalonia declared independence. This angered the government in Madrid, who dissolved Catalonian parliament and called a regional election on the 21st of December which the nationalist party won.
The division between Spain and Catalonia is clear, Catalonia wants independence and the Spanish government will not allow it. Whether or not Catalonia's different culture and language justify them to become a different country is open for debate, but an objective question that needs to be asked is the repercussions that the independence would have on Spain, Catalonia, and the world.
About 26% of Spain's exports come from Catalonia, 19% of Spain's GDP comes from Catalonia, and about 21% of foreign investment comes from Catalonia. For relatively small part of the country, from a land perspective, these numbers are large and would have negative consequences for the country of Spain, likely damaging their Spain's economy.
No country has expressed support for Catalonia seceding from Spain so there's no promise they would be recognized by anyone as a country. The European Union stands firmly behind Spain, so if Catalonia was to become independent they would presumably not be allowed in the EU, which also would mean they would not be able to use the euro, meaning they would have to create a new currency.
If you look at Brexit as a parallel for the situation that would (presumably) occur if Catalonia got their independence, the region would, as best put by the ING economist Geoffrey Minne, "plunge the region into a long period of uncertainty and would most probably be negative for the private sector." Not only would the Spanish and Catalan government be affected but the private sector would be affected as well, which greatly motivates the Western world to not support Catalan independence.
The risks and possible consequences are very clear and very real, but how much would Catalonia risk for their independence, how far will they go until they achieve independence, and if they do, what will it mean for the rest of the world?