During the The Vietnam War (1955-1975), the US used Napalm and Agent Orange as their major chemical weapons between 1965 and 1972. The US dropped more than 400,000 tons of Napalm on mostly civilian areas in Vietnam throughout the war.After the Baath regime in Syria had allegedly used chemical weapons against the civilian population in the suburbs of Damascus, the US decision makers accused the Syrian government of breaking an international agreement reached at the end of WW I. According to this agreement, chemical weapons are not permitted to be employed in any sort of military conflict. From the way the US leadership speaks, someone who is not familiar with world affairs may think that chemical weapons have not been used in wars from the end of WW I until the attacks of the Baath regime on August 21, 2013. Contrary to the image the US political leadership has been presenting recently, from WW II to today, the US has the lead in the world in the development, production and deployment of chemical weapons on both military forces and civilian populations at home and across the world.
Inside the US
In 2001, the San Francisco Chronicle reported that “at least three times in the past, San Franciscans and other Americans have been inadvertent victims of efforts designed to help shield citizens against attacks.”  In 1950, after the Army secretly sprayed supposedly harmless bacteria over the entire city and its suburbs by using a Navy ship cruising just outside the Golden Gate, germs in San Francisco made eleven people sick, one of whom died later. The CIA sent out agents from 1956 to 1961 to examine the effects of mind-altering drugs such as LSD and synthetic mescaline on unsuspecting people in San Francisco, Mill Valley and other cities across the country, in a secret behavior modification program called MK-ULTRA. Many of the victims hallucinated, many became sick and at least two deaths resulted from the experiments. Furthermore, from 1944 to 1974, hundreds of secret experiments in San Francisco and around the country were conducted by both the Defense Department and the Atomic Energy Commission which exposed unsuspecting patients to dangerous doses of radiation, including injections of plutonium.
By these secret research projects, the military and other federal agencies supposedly aimed at helping to prepare defenses against biological warfare, nuclear terror and mass brainwashing. Besides, in 1951, racist experiments were carried out by U.S. Army researchers by deliberately exposing African-Americans to the fungus Aspergillus fumigatus so as to discern whether they are more susceptible to the infections caused by such organisms than people of white European descent. Also within the same year, black workers at the Norfolk Supply Center in Virginia were exposed to crates contaminated with A. fumigatus spores. And others have followed the suit! 
READ MORE: http://www.worldbulletin.net/news/117150/a-very-brief-history-of-the-us-use-of-chemical-weapons