The cultural influence of the September 11 attacks (9/11) has been profound and long-lasting. The impact of 9/11 has extended beyond geopolitics into society and culture in general. Immediate responses to 9/11 included greater focus on home life and time spent with family, higher church attendance, and increased expressions of patriotism such as the flying of American flags. The radio industry responded by removing certain songs from playlists, and the attacks have subsequently been used as background, narrative or thematic elements in film, television, music and literature. Already-running television shows as well as programs developed after 9/11 have reflected post-9/11 cultural concerns. 9/11 conspiracy theories have become social phenomena, despite lack of support from scientists, engineers, and historians. 9/11 has also had a major impact on the religious faith of many individuals; for some it strengthened, to find consolation to cope with the loss of loved ones and overcome their grief; others started to question their faith or lost it entirely, because they could not reconcile it with their view of religion.
The culture of the United States succeeding the attacks is noted for heightened security and an increased demand thereof, as well as paranoia and anxiety regarding future terrorist attacks that includes most of the nation. Psychologists have also confirmed that there has been an increased amount of national anxiety in commercial air travel.
Due to the significance of the attacks, media coverage was extensive, including disturbing live pictures, and prolonged discourse about the attacks in general, resulting in iconography and greater meaning associated with the event. Don DeLillo called it "the defining event of our time". The attacks spawned a number of catchphrases, terms, and slogans, many of which continue to be used more than a decade later.
Through an endless reproductions in mass media and popular culture the attacks have an important cultural meaning for many people: "The attacks percolate as a central theme or historical backdrop in countless works of art, which bear witness to the complexity of 9/11 as historical, political, and media event, and contribute to the negotiation of its cultural meaning."  Regarding the attacks of 9/11 and Pearl Harbor Arthur G. Neal said:
"We create the world through our perceptions of it and seek to maintain that world in a manner consistent with our beliefs about it. It is through such symbolic constructions that we are provided with usable frameworks for shaping our memories and organizing them into coherent systems of meaning."
After the September 11 attacks, some movies and TV shows deleted scenes or episodes set within the World Trade Center. For example, The Simpsons episode "The City of New York vs. Homer Simpson", which first aired in 1997, was removed from syndication after the attacks because a scene showed the World Trade Center. Songs that mentioned the World Trade Center were no longer aired on radio, and the release dates of some films, such as the 2002 films Sidewalks of New York, People I Know, and Spider-Man, were delayed so producers could remove scenes that included the World Trade Center. The 2001 film Kissing Jessica Stein, which was shown at the Toronto International Film Festival the day before the attacks, had to be modified before its general public release, so the filmmakers could delete the scenes that depicted the World Trade Center.
Other episodes and films mentioned the attacks directly, or depicted the World Trade Center in alternate contexts. The production of some family-oriented films was also sped up due to a large demand for that genre following the attacks. Demand for horror and action films decreased, but within a short time demand returned to normal. By the first anniversary of the attacks, over sixty "memorial films" had been created. Filmmakers were criticized for removing scenes related to the World Trade Center. Rita Kempley of The Washington Post said "if we erase the towers from our art, we erase it [sic] from our memories". Author Donald Langmead compared the phenomenon to the 1949 novel Nineteen Eighty-Four, where historic mentions of events are retroactively "rectified". Other filmmakers such as Michael Bay, who directed the 1998 film Armageddon, opposed retroactively removing references to the World Trade Center based on post-9/11 attitudes.
Oliver Stone's film World Trade Center—the first movie that specifically examined the effects of the attacks on the World Trade Center, as contrasted with the effects elsewhere—was released in 2006. Several years after the attacks, works such as "The City of New York vs. Homer Simpson" were placed back in syndication. The National September 11 Museum has preserved many of the works that feature depictions of the original World Trade Center.
American comic books have always carried patriotic tones, especially during the Cold War—perhaps the most notable example is the character Captain America. 9/11 shifted the political climate and with it re-centered the public's attention on Muslims. Perhaps the most mainstream example of the influence 9/11 had on comic books is Iron Man, who was previously an anti-communist crusader; his canon was rewritten in comics after 9/11 and in the widely popular 2008 film Iron Man. In the film billionaire Tony Stark learns his weapons were sold without his knowledge to various terrorist groups after he was kidnapped and tortured in Afghanistan.
The September 11 attacks gained an iconographic meaning. This was due to the fact that the Twin Towers of the World Trade Center in New York City were portrayed as symbolic buildings representing American financial power, and the Pentagon in Arlington County, Virginia was portrayed as a symbolic building representing American military power. Backed up by the media and literature, many people see 9/11 as an attack on the economic and military power of America. Furthermore, the attacks are often pictured as a symbol for an era of war and terrorism.
Various slogans and captions were employed by media outlets to brand coverage of the September 11 terrorist attack, its after effects, and the U.S. government response. The slogans for American media were typically positioned on the bottom third of television broadcasts, or as banners across the top of newspaper pages. Designs typically incorporated a patriotic red, white, and blue motif, along with an explicit graphic of the American flag. Examples include:
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