For instance, the Catalunya Parliament has a requirement of 2/3 of the votes to changes its 'statut' (kind or regional constitution). But they will secede with a simple majority.

People also have the right to remain. It is not clear that a majority wants to secede, the percentages are close to 50% though. So want happens with the rest of the people. Besides the independent Catalunya movement does not apply that freedom to its regions and considers Catalunya indivisible (For instance they deny the right of Tarragona to secede an hypothetical Catalunya state https://youtu.be/3eS-j9Wx8lw?t=999).

But it's my understanding that most people didn't vote against seceding either, which does not mean that they want to stay.

Well it is not so easy. First, they will need to modify the constitution, which requires being approved a qualified majority not a simple one in parliament, in this case, is 3/5 of the parliament this reform might need to be approved by referendum (all the country not just Catalunya) in case a tenth of the parliament requires it. Second, the government has no desire to modify the current regional system, which is in line with its voters. Anyway the Canada case is not the norm and similar legislation are in use in other countries, for instance in Germany. https://www.thelocal.de/20170103/bavaria-must-remain-part-of...

Except, Germany previously did allow regions to leave.

There was a huge political situation after WWI about that, but in the end 5 countries agreed to allow the counties in the north of Germany to choose if they want to belong to Denmark or Germany.

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