Tourists are fascinated by the heavy blue cobblestones that pave the streets of Old San Juan. Why they are there is as good an explanation as any for Puerto Rico's current crisis. In the days of Spanish colonialism, they were ballast to keep the ships crossing the Atlantic from tossing about and blowing over. The ships came empty, and left for Spain full of gold, silver, and other riches stolen from the indigenous Taínos. The ballast left behind was used to pave the streets.… Puerto Rico has been sacked by colonial powers for half a millennium. Is it any wonder it is in dire straits? Today, it is $73 billion in debt.