Catalan lawmakers voted to go ahead with an Oct. 1 referendum on separating from Spain. Spain's constitutional court declared the vote suspended. And Catalan politicians said they would proceed anyway.

On Monday, Catalonia's national day, hundreds of thousands of independence-minded citizens are expected to take to the streets of Barcelona in a show of force, further roiling the waters.

If it all sounds like a recipe for an unpredictable and chaotic political crisis that threatens to push Spain into uncharted territory, it is.

"This has gotten out of control," said Javier Solana, Spain's former foreign minister and a former secretary-general of NATO. "We're no longer in a normal situation of political conflict, where the politicians fight but at least respect the rules of the game."

Just weeks ago, Catalonia was the scene of a terrorist attack that killed 16 people, most of them when a van ran over pedestrians on Barcelona's main promenade. The show of unity that followed was but a brief spasm, it turned out.