Spain is sovereign.
Two problems really stick out:
There was no referendum of the whole country.
“On 9 November 2015, Catalan lawmakers approved a plan for secession from Spain by 2017 with a majority vote 72 to 63. “ (Wiki)
That should have passed by a super-majority.
Two problems really stick out:
There was no referendum of the whole country.
If I recall correctly, the people of England weren’t asked for their approval in 1776 either....