The U.S. Declaration of Independence on secession:
Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn that mankind are more disposed to suffer, while evils are sufferable than to right themselves by abolishing the forms to which they are accustomed. But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government, and to provide new Guards for their future security.
In other words, Thomas Jefferson (and his co-authors) warned that independence movements are more likely to result in outcomes that are worse for the people than their current state, and that secession movements should be narrowly focused toward situations of despotism.
As far as I can tell, Catalonia is a wealthy region of a democratic and wealthy country. Of course, the 20th century was a crazy one for Spain, but for 40+ years, I'm not aware of any particular abuses of the Catalan people. The main arguments I've heard for secession are that Catalonia provides 16% of the population but 19% of GDP and doesn't get its tax revenue back, net-net, and oh yeah, Barcelona and Madrid are bitter football rivals. These are basically grounds for many states in the U.S. to secede.
What am I missing here? What are these great abuses that the Catalonian people are suffering that would inspire people to risk their livelihood and maybe even their very lives? Can some Europeans or knowledgeable Americans fill me in? Seems to me that the idea of tyranny has shifted radically from the era of the Soviet Union.