Madrid—The Catalonia crisis has reached its peak.

On Tuesday, the Catalan Parliament signed a unilateral declaration of independence.  It came in the wake of an illegal and highly contentious referendum in which 90% of voters chose independence, but the turnout was just 43%.

Catalan President Carles Puigdemont, however, suspended the implementation of the declaration for the sake of discussions.

Spanish Prime Minister Mariano Rajoy responded with an ultimatum: The separatists have five days to decide if they have actually declared independence or not.  If they have, they will be given an additional three days to withdraw it.

Thereafter, diplomacy will cease, and Article 155 of the constitution will be invoked.

What does this mean?

Although a Parliamentary Monarchy, Spain is operating under a sort of federal system, much like the U.S.   It’s comprised of 17 autonomous regions, Catalonia is one of them, that have their own governments and enjoy varying levels of autonomy.

Article 155, which has been described as “the atomic bomb,” can revert this autonomy and impose direct rule from the national government in Madrid.