Trans World Airlines (TWA) was one of the largest United States commercial airlines from 1930 until its merger with American Airlines in 2001. TWA had hubs in St. Louis New York City (JFK) and Atlanta with focus cities in Kansas City; San Juan Puerto Rico; and Los Angeles. Flying to most major U.S. cities TWA was one of the largest domestic airlines; before deregulation it and American United and Eastern were known as the Big Four.