Final answer:
Leon Czolgosz assassinated President McKinley because he viewed him as a symbol of oppression and a threat to the working class, in line with the broader anarchist movement's goals to challenge power structures.
Step-by-step explanation:
Leon Czolgosz decided to assassinate President William McKinley because he believed McKinley was a threat to the working class. As an anarchist, Czolgosz saw the president as a symbol of oppression by the government and the business monopolies that, in his view, exploited the majority for the benefit of the wealthy few. Czolgosz's act was part of a broader wave of anarchist political violence during that era, which sought to challenge existing power structures and promote radical societal change.