Governments usually do not like to give up the money making portions of their countries and neither does the population of the rest of the country. You never see a poor part of a country seceding (well, other than Quebec maybe).
Ireland from the UK, Slovakia from Czechoslovakia, Kosovo from Serbia, the bits of Poland that were in Austria-Hungary or Germany from those two empires, pretty much every single European overseas colonial possession... Not to mention all the widely-supported secessionist movements that have failed militarily in the Indian northeast, in the Chinese west, or in the Russian Caucasus.
Of course, Americans prefer to imagine that political conflict everywhere is all about money rather than actually confront the idea that people other than themselves have collective identities and cultures.
Maybe you were thinking about taxes ?
[1] "http://www.imf.org/external/pubs/ft/fandd/basics/gdp.htm"
But not only that, the centralisation of government powers and agencies have created a problem where many big companies have to be in Madrid even if most their operations are in other parts of the country. That makes their taxes to be paid in Madrid instead of e.g. Valencia, Bilbao or Barcelona. The amount of taxes lost because of this is HUGE and much worse than the 16 billion per year above.
An independence would bring back 100% of the former and a good chunk of the latter. Hopefully that would help Catalonia grow at the pace its economy can and then it should be able to contribute back to Europe much more than now. Contributions have to be sustainable.
Edit: This comment is now at -1. Please argue instead of downvoting. You're acting against HN's rules.
In the Catalan media they appear in waves, polluting all the comments and making the discussion unbearable.
They are also holding cyberatacks to the Catalan News Agency so we cannot inform outside.
They have also closed aerial space, so drones cannot fly and take pictures of massive demonstrations tomorrow if we cannot vote.
Google censors an app from Google Play which was telling people where to vote, after Spanish court forces it: https://twitter.com/thespainreport/status/913798991539777537 https://twitter.com/JulianAssange/status/913812096319737857
And more geopolitical info: https://twitter.com/JulianAssange/status/913920102411718656
Tech people in the world: Please help us and spread the word!
http://www.expansion.com/economia/2017/09/29/59cd50b8ca47412...
In the words of General Sherman:
You people of the South don't know what you are doing. This country will be drenched in blood, and God only knows how it will end. It is all folly, madness, a crime against civilization! You people speak so lightly of war; you don't know what you're talking about. War is a terrible thing! You mistake, too, the people of the North. They are a peaceable people but an earnest people, and they will fight, too. They are not going to let this country be destroyed without a mighty effort to save it… Besides, where are your men and appliances of war to contend against them? The North can make a steam engine, locomotive, or railway car; hardly a yard of cloth or pair of shoes can you make. You are rushing into war with one of the most powerful, ingeniously mechanical, and determined people on Earth — right at your doors. You are bound to fail. Only in your spirit and determination are you prepared for war. In all else you are totally unprepared, with a bad cause to start with. At first you will make headway, but as your limited resources begin to fail, shut out from the markets of Europe as you will be, your cause will begin to wane. If your people will but stop and think, they must see in the end that you will surely fail.
People are not rational however, and the wealthy landowners were facing the extinction of their wealth... so they started a war.
As someone who doesn't know much about American history: What happened to the wealth of those Southern landowners after the war? Did they get to keep it?
The South was still devastated by the war. But being largely agrarian to begin with, loss of capital wasn't quite as hard a blow as losing a factory.