The main cause of the Great Chicago Fire in 1871 is often debated, but it is widely believed to have started in a barn owned by the O'Leary family. Dry conditions, wooden structures, and strong winds rapidly spread the flames throughout the city. The fire destroyed a significant portion of Chicago, killing hundreds and leaving thousands homeless. The aftermath led to significant urban renewal and the establishment of stricter building codes. The disaster also underscored the need for improved fire-fighting measures and infrastructure, resulting in changes that shaped the future development of Chicago into a modern city.