8. President Woodrow Wilson believed in "moral diplomacy." Why did he send American forces into Mexico to pursue Francisco "Pancho" villa?

It is because Villa's forces raided Columbus, New Mexico and ended up killing 18 Americans.

President Woodrow Wilson sent American forces into Mexico to pursue Francisco "Pancho" Villa because this carried out an invasion to the American city of Columbus, killing many American citizens.

Explanation:

Before dawn on March 9, 1916, a group of approximately 1,500 men (the official report of the US Army mentioned between "500-700 participants") of the Villa army, under the command of General Ramon Banda Quesada, attacked the town from Columbus (New Mexico), in retaliation for the official recognition of the Carrancista regime by the United States and in search of the merchant Sam Ravel (a supplier who, according to Villa, had stolen him.) The invasion of Pancho Villa to New Mexico was the only invasion that the United States had in its territory since the Anglo-American War of 1812.

Faced with the events that took place in the Battle of Columbus, US President Woodrow Wilson sent on March 14, 1916 troops headed by General "Black Jack" Pershing (the same who would command US forces in World War I) to the capture of Villa. The search for Villa would eventually lead the American troops about 600 km into Mexican territory, reaching the city of Parral.

For eleven months, the ten thousand Pershing soldiers toured the deserts of the immense state of Chihuahua. Pershing managed to disperse the Mexican forces that had attacked Columbus, but Pancho Villa disappeared into the vast Mexican territory mocking his persecutors.