Populists believe that a democratic vote is king. Fair enough. But as everyone should know, we did away with absolute monarchs centuries ago. 

Even though a majority of a region's people may wish to separate from the mother nation, the separation itself must adhere to legal and human rights principles. Otherwise few outside nations will recognize the breakaway region as a legitimate entity. Instead it becomes a pariah state, one that has no respect for the accepted norms of democracy.

If a country's constitution has a defined procedure for secession, it must be followed. If no such constitutional procedure exists, the manner of the secession must instead be negotiated between the two parties. And in both cases the division of "assets" must be negotiated as well. It's an enormous undertaking that done properly will take a long time. Populists don't like that. They'd rather ignore the niceties and jump right to the finish.