Atlanta is the capital and most populous city of the U.S. state of Georgia. With an estimated 2019 population of 506,811, it is also the 37th most populous city in the United States. The city serves as the cultural and economic center of the Atlanta metropolitan area, home to more than 6 million people and the ninth-largest metropolitan area in the nation. Atlanta was originally founded as the terminus of a major state-sponsored railroad. With rapid expansion, however, it soon became the convergence point among multiple railroads, spurring its rapid growth. The city's name derives from that of the Western and Atlantic Railroad's local depot, signifying the town's growing reputation as a transportation hub. During the American Civil War, the city was almost entirely burned to the ground in General William T. Sherman's famous March to the Sea. However, the city rose from its ashes and quickly became a national center of commerce and the unofficial capital of the "New South". During the 1950s and 1960s, Atlanta became a major organizing center of the civil rights movement, with Dr. Martin Luther King Jr., Ralph David Abernathy, and many other locals playing major roles in the movement's leadership. During the modern era, Atlanta has attained international prominence as a major air transportation hub, with Hartsfield–Jackson Atlanta International Airport being the world's busiest airport by passenger traffic since 1998. It ranks in the top twenty among world cities and 10th in the nation with a gross domestic product (GDP) of $385 billion. Atlanta has topographic features that include rolling hills and dense tree coverage, earning it the nickname of "the city in a forest". Revitalization of Atlanta's neighborhoods, initially spurred by the 1996 Summer Olympics, has intensified in the 21st century, altering the city's demographics, politics, aesthetics, and culture.