Wikipedia says, "The burgeoning port and railroad industry, combined with oil discovery in 1901, has induced continual surges in Houston's population. In the mid-twentieth century, Houston became the home of the Texas Medical Center—the world's largest concentration of healthcare and research institutions—and NASA's Johnson Space Center, where the Mission Control Center is located. Rated as a global city, Houston's economy has a broad industrial base in energy, manufacturing, aeronautics, and transportation. It is also leading in healthcare sectors and building oilfield equipment; only New York City is home to more Fortune 500 headquarters."