 Complete the following phrase:  During the 1910s, relations between Mexico and the United States were often volatile. In 1912, U.S. President William Howard Taft considered sending an expeditionary force to protect foreign-owned property from damage during the Mexican Revolution. Thus War Plan Green was developed. In 1916, U.S. troops under General John Pershing invaded Mexico in search of Pancho Villa, whose army had attacked Columbus, New Mexico; earlier, American naval forces had 