1890-1920
The growth pattern of San Juan shifted once more after the US occupied and ultimately gained control of Puerto Rico in the Spanish-American War. The Americans brought with them vast improvement in the infrastructure of the island. Besides establishing a better road network and sanitation standards, many International and American businesses were drawn to the island as well.
Industrial growth centered in Rio Piedras, which was gradually becoming greater San Juan. American influence was also the reason behind the growth of the residential suburb, previously unknown in the unnucleated city structure.
Although improved, health and sanitary conditions near the Martin Pena canal (connecting San Juan Harbor to the San Jose Lagoon) were worse than in the rest of the city. The canal had been used for sewage by past residents, and becuase the water was standing, had been a breeding ground for illness.