ANTWERP, Belgium — As debt-burdened European governments struggle to overcome the disparities in their still-imperfect union, old demons of regional separatism have surged anew in recent months, raising another unwelcome challenge to the continent’s traditional nation-states.

Separatist movements have dramatically reinforced their positions here in Belgium’s prosperous Flanders region, where the independence-minded New Flemish Alliance captured Antwerp’s 16th-century City Hall on Oct. 14 and, under its populist leader Bart De Wever, is heading into national elections in 2014 with new wind in its sails.