 Meanwhile, Chicago's skyscraper industry also boomed during the decade before World War I.The city's elevated train network was operating by 1910, allowing more workers to come into the centre.In 1910 alone of new offices were opened and by the end of the decade, Chicago had the second largest number of headquarters offices in the U.S. Chicago architectural firms such as Daniel H. Burnham and then Graham, Anderson, Probst & White continued to design skyscrapers in the "palazzo" style made popular in the previous decade.