The reaction of the Spanish state seems way out of proportion to the threat to the Spanish state, either from Catalonia itself or from other independently-minded regions (e.g. Basque). The so-called referendum is demonstrably not a valid referendum, and there is no legal mechanism under the current Spanish constitution to implement it. So quite what the Spanish state is panicking about is a mystery. It would have been far better for the Spanish state to have engaged with the “referendum” and aided it to its futile ending instead of childishly banning the referendum and sending in the riot squads to enforce the ban. The tactic just hands the status of victimhood to the Catalonian separatists… some of whose obedience to the rule of law is questionable.
But the issue for Catalonia is a wider one for Spain. And, in turn, the issue for Spain is a wider one for the European Union.
Spain - the Spanish Union - like the European Union, is arguably an artificial construct, with no cultural ties between regions to naturalise the union. Nationalism - or regionalism? - has worsened already-negative and divergent emotionally-driven politics. The history of Catalonia and Spain offers no clear solutions to current generations. If anything, European (and Russian!) intervention in the Spanish peninsula has aggravated matters and extended long-held grievances between the regions of Spain.
It seems that the Spanish Union is as much as victim of the same old divide-and-rule method of the old Roman Empire within the European Union as it is the perpetrator of those same methods within the Spanish Union. Wheels within wheels.
Nevertheless, I perceive the Catalonian separatist movement as an instructive guide to the future of ordinary life within the Deep State of the Fully-Integrated European Union. If, as in Spain, separatism is de facto illegal (i.e. there is no legal provision for separatism and self-governance), grievances remain hard-baked into the political and economic system, government serves itself at the expense of the people, then the imposition of government for the sake of government - enforced by unwarranted and disproportionate brutality, revealing the fear of the governors - is simply going to create civil wars.
As a mere aside, the botched method the Catalonian separatists deployed to instigate the “referendum” has haunting parallels with how the British Conservative Party believes Brexit can - and apparently should - be possible.
An MEP’s view: https://beta.theglobeandmail.com/opinion/a-coup-against-spanish-democracy-is-a-coup-against-europe/article36449710/?ref=http://www.theglobeandmail.com&
Brookings Institute: https://www.brookings.edu/blog/order-from-chaos/2017/09/29/the-referendum-in-catalonia-explained/
Mainstream media comment (limited reportage, usual caveats of completeness and context apply):
History (of sorts, from Wikipedia, usual caveats apply):