The major historical event associated with the assassination of William McKinley is the rise of progressive reforms in the early 20th century. McKinley, who was assassinated in 1901 by anarchist Leon Czolgosz, was succeeded by Theodore Roosevelt. Roosevelt's presidency marked a transformational period characterized by significant social and political changes, including the regulation of monopolies, labor rights, and environmental conservation. McKinley’s assassination highlighted the political violence of the era and contributed to the growing public demand for reforms aimed at addressing social inequalities and economic injustices, leading to the Progressive Era's initiatives.