Question: Windows on the World was a complex of venues on the top floors (106th and 107th) of the North Tower (Building One) of the original World Trade Center complex in Lower Manhattan that included a restaurant called Windows on the World, it operated until 2001 when they were destroyed in the September 11 attacks (also referred to as 9/11) were a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda on which country?

Context paragraphs:
World Trade Center (1973–2001): The original World Trade Center was a large complex of seven buildings in Lower Manhattan, New York City, United States.  It featured the landmark twin towers, which opened on April 4, 1973, and were destroyed as a result of the September 11 attacks in 2001.  At the time of their completion, the "Twin Towers"—the original 1 World Trade Center, at 1368 ft ; and 2 World Trade Center, at 1,362 ft —were the tallest buildings in the world.  The other buildings in the complex included the Marriott World Trade Center (3 WTC), 4 WTC, 5 WTC, 6 WTC, and 7 WTC.  All these buildings were built between 1975 and 1985, with a construction cost of $400 million ($ in 2014 dollars).  The complex was located in New York City's Financial District and contained 13400000 sqft of office space.

September 11 attacks: The September 11 attacks (also referred to as 9/11) were a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda on the United States on the morning of Tuesday, September 11, 2001.  The attacks killed 2,996 people, injured over 6,000 others, and caused at least $10 billion in infrastructure and property damage. <ref name="PEARL9/11"> </ref>

Windows on the World: Windows on the World was a complex of venues on the top floors (106th and 107th) of the North Tower (Building One) of the original World Trade Center complex in Lower Manhattan that included a restaurant called Windows on the World, a smaller restaurant called Wild Blue, a bar called The Greatest Bar on Earth, and rooms for private functions.  Developed by restaurateur Joe Baum and designed initially by Warren Platner, Windows on the World occupied 50,000 square feet (4,600 m²) of space in the North Tower.  The restaurants operated from April 19, 1976, until 2001 when they were destroyed in the September 11 attacks.

Six World Trade Center: Six World Trade Center was an eight-story building in Lower Manhattan in New York City.  It opened in 1973 and was the building in the World Trade Center complex that had the fewest stories.  The building served as the U.S. Customs House for New York.  It was destroyed in 2001 due to the collapse of the North Tower during the September 11 attacks; it is not set to be replaced as part of the new World Trade Center.

Marriott World Trade Center: The Marriott World Trade Center was a 22-story steel-framed hotel building with 825 rooms.  It opened in July 1981 as the Vista International Hotel and was located at 3 World Trade Center in Manhattan, New York City, with the World Trade Center complex having its own zip code of 10048.  The hotel no longer operates and was destroyed beyond repair as a result of the terrorist attacks of September 11, 2001, after the collapse of the Twin Towers.  The hotel will not be replaced as part of the new World Trade Center complex, but will rather share its name with the new office tower.

Westfield World Trade Center: Westfield World Trade Center is a shopping center at the World Trade Center complex in Manhattan, New York, United States, which is operated and managed by Westfield Corporation.  The mall opened on August 16, 2016, replacing an earlier shopping center at the same location called The Mall at the World Trade Center, which was located in the concourse area of the original World Trade Center complex until it was destroyed during the September 11 attacks.

Collapse of the World Trade Center: The Twin Towers of the World Trade Center collapsed on September 11, 2001, as a result of being struck by two jet airliners hijacked by 10 terrorists affiliated with al-Qaeda, during the September 11 attacks.  Two of the four hijacked airliners crashed into the Twin Towers, one into the North Tower (1 World Trade Center) and the other into the South Tower (2 World Trade Center).  The collapse of the Twin Towers destroyed the rest of the complex, and debris from the collapsing towers severely damaged or destroyed more than a dozen other adjacent and nearby structures.  The South Tower collapsed at 9:59 am, less than an hour after being hit by the second hijacked airliner, and at 10:28 am the North Tower collapsed.  Later that day, 7 World Trade Center collapsed at 5:21 pm from fires that had started when the North Tower collapsed.  As a result of the attacks to the towers, a total of 2,763 people died.  Of the people who died in the towers, 2,192 were civilians, 343 were firefighters, and 71 law enforcement officers. Aboard the two airplanes, 147 civilians and 10 hijackers also died.

7 World Trade Center: 7 World Trade Center (7 WTC) refers to two buildings that have existed at the same location within the World Trade Center site in Lower Manhattan, New York City.  The current structure is the second building to bear that name and address in the World Trade Center complex.  The original structure, part of the original World Trade Center, was completed in 1987 and was destroyed in the September 11 attacks.  The current building opened in May 2006.  Both buildings were developed by Larry Silverstein, who holds a ground lease for the site from the Port Authority of New York and New Jersey.

One World Trade Center: One World Trade Center (also known as 1 World Trade Center, 1 WTC or Freedom Tower ) is the main building of the rebuilt World Trade Center complex in Lower Manhattan, New York City.  It is the tallest building in the Western Hemisphere, and the sixth-tallest in the world.  The supertall structure has the same name as the North Tower of the original World Trade Center, which was destroyed in the terrorist attacks of September 11, 2001.  The new skyscraper stands on the northwest corner of the 16 acre World Trade Center site, on the site of the original 6 World Trade Center.  The building is bounded by West Street to the west, Vesey Street to the north, Fulton Street to the south, and Washington Street to the east.

World Trade Center site: The World Trade Center site, formerly known as "Ground Zero" after the September 11 attacks, is a 14.6-acre (5.9 ha) area in Lower Manhattan in New York City.  The previous World Trade Center complex stood on the site until it was destroyed in the September 11 attacks.  The Port Authority of New York and New Jersey (PANYNJ), Silverstein Properties, and the Lower Manhattan Development Corporation (LMDC) oversee the reconstruction of the site according to a master plan by Studio Daniel Libeskind.  The site is bounded by Vesey Street to the north, the West Side Highway to the west, Liberty Street to the south, and Church Street to the east.  The Port Authority owns the site's land (except for 7 World Trade Center).  Developer Larry Silverstein holds the lease to retail and office space in four of the site's buildings.

Supporting paragraphs: Windows on the World September 11 attacks
Answer: United States