<P> The ratification of the 18th amendment to the Constitution in 1919 made the production and sale (including exportation) of alcoholic beverages illegal in the United States . This ushered in the beginning of what is known as the Gangster Era, a time that roughly spans from 1919 until 1933 when Prohibition was repealed . The 1920s saw gangsters, including Al Capone, Dion O'Banion, Bugs Moran and Tony Accardo battle law enforcement and each other on the streets of Chicago during the Prohibition era . Chicago was the location of the infamous St. Valentine's Day Massacre in 1929, when Al Capone sent men to gun down members of a rival gang, North Side, led by Bugs Moran . </P> <P> In 1924, Chicago was the first American city to have a homosexual - rights organization, the Society for Human Rights . This organization produced the first American publication for homosexuals, Friendship and Freedom . Police and political pressure caused the organization to disband . </P> <P> In 1933, Chicago Mayor Anton Cermak was fatally wounded in Miami, Florida, during a failed assassination attempt on President - elect Franklin D. Roosevelt . In 1933 and 1934, the city celebrated its centennial by hosting the Century of Progress International Exposition Worlds Fair . The theme of the fair was technological innovation over the century since Chicago's founding . </P> <P> On December 2, 1942, physicist Enrico Fermi conducted the world's first controlled nuclear reaction at the University of Chicago as part of the top - secret Manhattan Project . This led to the creation of the atomic bomb by the United States, which it used in World War II in 1945 . </P>

What two offices can be found in 207 calhoun st (yellow building beside the library)