the third largest US city. It is in the state of Illinois on Lake Michigan and is sometimes called the 'Windy City'. It had the world's first skyscrapers. Chicago is the centre of the American Middle West and its O'Hare airport is one of the busiest airports in the world. The El train runs around the business district, called the Loop. During Prohibition, Chicago was known for its gangsters (= criminals), especially Al Capone.