World War I began in Europe in 1914 the United States remained neutral before 6 April 1917 when President Woodrow Wilson signed the joint resolution declaring that a state of war currently existed between the United States of America and Imperial Germany. Three months later, in August 1917, U. S. National Guard units from twenty-six states and the District of Columbia United to make the 42nd Division of the United States Army. Douglas MacArthur, serving as Chief of Staff for the Division, commented that it would extend over the whole country like a rainbow. This way, the 42nd became known as the Rainbow Division.
It included four infantry regiments in New York, Ohio, Alabama, and Iowa. Men from many other countries, among them New Hampshire, Massachusetts, Indiana, Michigan, Rhode Island, Maryland, California, South Carolina, Missouri, Connecticut, Tennessee, New Jersey, Colorado, Maine, North Carolina, Kansas, Texas, Wisconsin, Texas, Illinois, Minnesota, Oklahoma, Nebraska, Oregon, and Pennsylvania also joined the branch and became machine gunners, ambulance drivers, worked in field hospitals, or even served in the military police.