20th century

The construction of the New York City Subway, which opened in 1904, helped bind the new city together, as did additional bridges to Brooklyn. In the 1920s Manhattan experienced large arrivals of African-Americans as part of the Great Migration from the southern United States, and the Harlem Renaissance, part of a larger boom time in the Prohibition era that included new skyscrapers competing for the skyline. New York City became the most populous city in the world in 1925, overtaking London, which had reigned for a century.^[78] Manhattan's majority white ethnic group declined from 98.7% in 1900 to 58.3% by 1990.^[79]
On March 25, 1911, the Triangle Shirtwaist Factory fire in Greenwich Village killed 146 garment workers. The disaster eventually led to overhauls of the city's fire department, building codes, and workplace regulations.^[80]
The period between the World Wars saw the election of reformist mayor Fiorello La Guardia and the fall of Tammany Hall after 80 years of political dominance.^[81] As the city's demographics stabilized, labor unionization brought new protections and affluence to the working class, the city's government and infrastructure underwent a dramatic overhaul under La Guardia. Despite the Great Depression, some of the world's tallest skyscrapers were completed in Manhattan during the 1930s, including numerous Art Deco masterpieces that are still part of the city's skyline today, most notably the Empire State Building, the Chrysler Building, and the GE Building.

Victory over Japan Day in Times Square, 1945

Returning World War II veterans created a postwar economic boom, which led to the development of huge housing developments targeted at returning veterans, the largest being Peter Cooper Village-Stuyvesant Town, which opened in 1947.^[82] In 1952, the UN relocated from its first headquarters near Queens, to the East Side of Manhattan.^[83]
The Stonewall riots were a series of spontaneous, violent demonstrations by members of the gay community against a police raid that took place in the early morning hours of June 28, 1969, at the Stonewall Inn in the Greenwich Village neighborhood of Lower Manhattan. They are widely considered to constitute the single most important event leading to the gay liberation movement and the modern fight for LGBT rights in the United States.^[84][85]
In the 1970s job losses due to industrial restructuring caused New York City, including Manhattan, to suffer from economic problems and rising crime rates.^[86] While a resurgence in the financial industry greatly improved the city's economic health in the 1980s, New York's crime rate continued to increase through the decade and into the beginning of the 1990s.^[87]
The 1980s saw a rebirth of Wall Street, and Manhattan reclaimed its role at the center of the worldwide financial industry. The 1980s also saw Manhattan at the heart of the AIDS crisis, with Greenwich Village at its epicenter. The organizations Gay Men's Health Crisis (GMHC) and AIDS Coalition to Unleash Power (ACT UP) were founded to advocate on behalf of those stricken with the disease.
By the 1990s crime rates started to drop dramatically due to revised police strategies, improving economic opportunities, gentrification, and new residents, both American transplants and new immigrants from Asia and Latin America. Murder rates that had reached 2,245 in 1990 plummeted to 537 by 2008, and the crack epidemic and its associated drug-related violence came under greater control.^[88] The outflow of population turned around, as the city once again became the destination of immigrants from around the world, joining with low interest rates and Wall Street bonuses to fuel the growth of the real estate market.^[89] Important new sectors, such as Silicon Alley, emerged in Manhattan's economy.

The newly completed Singer Building towering above the city, 1909  A construction worker on top of the Empire State Building as it was being built in 1930. To the right, is the Chrysler Building.  The Stonewall Inn in Greenwich Village, a designated U.S. National Historic Landmark and National Monument, as the site of the 1969 Stonewall Riots.[28][90]  United Airlines Flight 175 hits the South Tower of the first World Trade Center on September 11, 2001.

21st century

Flooding on Avenue C caused by Hurricane Sandy on October 29, 2012^[91]

On September 11, 2001, two of four hijacked planes were flown into the Twin Towers of the original World Trade Center, and the towers subsequently collapsed. 7 World Trade Center collapsed due to fires and structural damage caused by heavy debris falling from the collapse of the Twin Towers. The other buildings within the World Trade Center complex were damaged beyond repair and soon after demolished. The collapse of the Twin Towers caused extensive damage to other surrounding buildings and skyscrapers in Lower Manhattan, and resulted in the deaths of 2,606 people, in addition to those on the planes. Since 2001, most of Lower Manhattan has been restored, although there has been controversy surrounding the rebuilding. Many rescue workers and residents of the area developed several life-threatening illnesses that have led to some of their subsequent deaths.^[92] A memorial at the site was opened to the public on September 11, 2011, and the museum opened in 2014. In 2014, the new One World Trade Center, at 1,776 feet (541 m) and formerly known as the Freedom Tower, became the tallest building in the Western Hemisphere,^[93] while other skyscrapers were under construction at the site.
The Occupy Wall Street protests in Zuccotti Park in the Financial District of Lower Manhattan began on September 17, 2011, receiving global attention and spawning the Occupy movement against social and economic inequality worldwide.^[94]
On October 29 and 30, 2012, Hurricane Sandy caused extensive destruction in the borough, ravaging portions of Lower Manhattan with record-high storm surge from New York Harbor,^[95] severe flooding, and high winds, causing power outages for hundreds of thousands of city residents^[96] and leading to gasoline shortages^[97] and disruption of mass transit systems.^{[98][99][100][101]} The storm and its profound impacts have prompted the discussion of constructing seawalls and other coastal barriers around the shorelines of the borough and the metropolitan area to minimize the risk of destructive consequences from another such event in the future.^[102]