The best answer to how the Spanish-American War contributed to concerns that the United States might become an imperialistic power is:
C. The United States struggled to reconcile retaining power over the Philippines while Filipinos wished to be independent.
This reflects the tension between American expansionism and the desire of the Filipino people for independence, highlighting concerns about the implications of U.S. territorial acquisitions and control over other nations. The situation in the Philippines raised questions about the morality and legitimacy of American rule and whether the U.S. would become an imperial power.