Detroit is the most populous city in the U.S. state of Michigan and the largest city on the United States-Canada border. It is the seat of Wayne County, the most populous county in the state. It is a primary business, cultural, financial and transportation center in the Metro Detroit area, a region of 5.2 million people, and serves as a major port on the Detroit River connecting the Great Lakes system to the Saint Lawrence Seaway. It was founded on July 24, 1701, by the French explorer and adventurer Antoine Laumet de La Mothe, sieur de Cadillac.The Detroit area emerged as a significant metropolitan region within the United States as construction of a regional freeway system was completed in the 1950s and 1960s. With these commuting ties allowing social and economic integration across a larger area, the Detroit name sometimes refers to the three-county Urban Area, the six-county Metropolitan Statistical Area, or the nine-county Combined Statistical Area. The Detroit–Windsor area, a commercial link straddling the Canada–U.S. border, has a total population of about 5,700,000. The Detroit metropolitan region currently holds roughly one-half of the state's population. The D, Hockeytown (a trademark owned by the city's NHL club, the Red Wings), Rock City (after the Kiss song "Detroit Rock City"), and The 313 (its telephone area code). Detroit's auto industry was an important element of the American "Arsenal of Democracy" supporting the Allied powers during World War II.