What was the most significant event in U.S. history in 1911?

The most significant event in U.S. history in 1911 was the Triangle Shirtwaist Factory fire in New York City. This tragic incident resulted in the deaths of 146 garment workers, primarily young immigrant women, due to inadequate safety measures and locked exit doors. The fire highlighted the dangerous working conditions in factories and spurred significant reforms in labor laws and workplace safety regulations across the country. It also galvanized the labor movement and raised public awareness about workers' rights.