Santurce - San Juan, Spanish explorer Juan Ponce de León founded San Juan in 1521, and the city became one of the most strategic outposts in the New World, easy to defend because of its elevated island geography, more or less mosquito-free due to the constant whirring of the trade winds, and a sentinel over the most protected harbor in the Caribbean. Over the next century it underwent massive fortification to protect it from British and Dutch maritime incursions, as the Spanish government identified the settlement as the linchpin in its domination of the sea routes between Europe and America. Trade in sugar, coffee, cotton, tobacco and African slaves flourished in the 16th and 17th centuries. Smuggling and the rise of a plantation-owning bourgeoisie weakened Spain's grip on the city, and San Juan began developing a distinct identity during the 18th century. For the most part, the city remained a monumental, remote military base for Spain, its development slowed by the Spanish government's monopoly laws, until the USA claimed Puerto Rico as victor's spoils following the Spanish-American War in 1898.

Nationalist fervor spread through the 19th century, only to be stopped in its tracks in 1897 by the US occupation during the Spanish-American war. The US recognized the port as the safest in the Caribbean, and soon shipping terminals grew up around the bay, new roads spread out to the rest of the island, and agricultural goods such as sugar, tobacco and coffee flowed into the port from other parts of the island for export. Along with the rest of their compatriots, Sanjuaneros received US citizenship in 1917 - just in time to get drafted for WWI. Partly from an infusion of American cash during the 1940s (consisting largely of tax breaks to resident US companies), San Juan grew rapidly, annexing suburbs like Santurce, Condado and Miramar. Tourism became a major earner.