Why did the United States decide to enter World War I? * A. The United States had suffered economically from European sanctions. B. A European nation had taken aggressive actions against the United States C. The U. S. President was obligated to fulfill election campaign promises D. Communist activities among U. S. Immigrants were threatening the country.

B. A European nation had taken aggressive actions against the United States

Explanation:

Germany took aggressive action against the USA, which caused the American government to declare war on Germany, entering WW1 in 1917.

Before that, Germany attacked American ships that were sailing towards England, killing many Americans. However, Germany sank a British civilian ship, where it had a group of American passengers who died due to the attack. In addition, Germany was fervently encouraging Mexico to attack the United States.