Anti-Americanism is hostility towards the people, policies and culture of the United States of America.
Many Islamic and Marxist regimes are noted for their anti-American sentiments - often disguised as criticism of the War on Terror. Those with anti-American sentiments often lack the liberty celebrated in America and therefore hate America because of the freedoms available to the American people. Many anti-Americans, which include even some American citizens, are liberals who believe that other nations are equal to or beyond America in their achievements. There are some others who envy America's military might and ability to spread democracy who dislike America for doing so.
"Anti-Americanism is not only the world’s most pernicious and ubiquitous ideology — it is also the most tenacious. In fact, it has taken on some aspects of a religion." 
"Anti-Americanism is the prevailing disease of intellectuals today." 
Anti-Americanism and the Liberal Anti-Self-Defense Movement
Many Anti-American people, both in the USA and abroad, are hoplophobic and thus usually attempt to demonize America's support of all the world's peoples' unalienable rights to home security, self-defense, and to being liberty's final bulwark of armed defense against the police state tyranny of constant big government expansion.
These vitriolic Anti-American leftists demonize American conservatives, many American Christians, many conservative Asian-born Buddhists (who escaped Communism to the liberty of America), most American veterans (despite those veterans having defended their European and Asian nations from both National Socialism during World War II and Communism during the Cold War), most American Patriots, almost all American preppers, all American gun enthusiasts, many American libertarians and some more moderate American liberals who invest in and use firearms.
Criminals by Nature Never Follow Laws
"Criminals never follow laws" -- especially progressive police state created gun control, ammunition control and gun free zone laws. These anti-American anti-Second Amendment gun control, ammunition control and gun free zones have always been absurd left wing "unicorn utopia" Pollyanna fantasies of the Anti-self-defense movement for the simple reason that criminals by their nature never follow laws.
Anti-Americanism and anti-war
For a more detailed treatment, see Anti-war.
A large part of the anti-war movement during the Vietnam War dealt with promoting anti-Americanism, often being used to root for the enemy such as the Vietcong, and later al Qaeda.