We were never really “neutral”, we pretty much relied on the Royal Navy for the Atlantic, because we were beefing up our Pacific Fleet, after we acquired Hawaii and The Philippines, after the Spanish-American War, and even then it was thought a showdown with Japan was inevitable, even though they were technically an “ally” during WWI.
The U.S. was not an active belligerent prior to 1917. The U.S. in 1917 had the world’s largest economy and possessed vast military potential. Though not nearly as large or decisive as U.S. involvement in World War II, the U.S. active participation did shift the balance of power in the West to the side of the Allies.