This map shows the European regions fighting to achieve independence
@ hellsbrink suggested in the Catalan Independence? Democracy dies in Spain thread that a thread on separatist movements across the EU would be a good idea. A quick google brought up the map above with its patchwork of Medieval statelets. Note that some of the regions depicted are outside the EU.
It is immediately obvious why Spain is dead set against Catalonian independence since the country is home to at least half a dozen separatist movements to one extent or another. A Catalonian secession would probably bring about a domino effect. A further complication is that a couple of the prospective states lay claim to bits of France.
France, Italy, Belgium, the Netherlands and Germany also have regions that would like a bit more independence. Belgium is a relatively recent creation that cobbled together two quite disparate regions into one country. The 2010 general election in Belgium produced a result that led to 541 days of negotiations before a government was formed. Germany is an even more recent creation with a federation of German states coalescing in 1871 to form the German Empire.
Closer to home Ireland led the way in the 1920s by breaking away from the UK, with the noted exception of the bothersome bit in the north east. Scotland will probably vote itself out of the Union at some stage depending on how they fare economically, post-Brexit.
Given the above it’s no wonder that the EU is less than enthusiastic about Catalonian independence. It’s difficult enough steadying the ship during the Brexit process without the entire continent balkanising. The thought of the the Eurozone's fourth largest economy breaking into half a dozen unsustainable states might be music to the ears of Nigel Farage but it must be causing some sleepless nights in Brussels and Berlin.