Iquique was the undisputed capital of the saltpeter, or nitrate industry from the 1860s to 1920. The town's historic center evinces this period with its many fine palatial buildings. After the Germans invented chemical fertilizer shortly before WWII, the nitrate industry collapsed and the city fell into decay. Today Iquique's economy is supported by its fishing industry and its tax free status. Driving outside the city into the desert, one can find many interesting well-preserved ghost towns that remain from the nitrate industry's hey-day. Some, including Humberstone, are now classified national monuments.