Compared to the European combatants of World War I, imperialism did not play a major role in the US deciding to enter the war. One could argue that imperialism played an indirect role through the Zimmerman note, where Germany offered to help Mexico gain back land lost during the Mexican-American War. This outraged many around the country, but it was viewed more as meddling and less of a credible threat.
Imperialism played another indirect role in American entry into the war since the Spanish-American War demonstrated that the United States had modernized its navy and could project power abroad. This made the United States a potential ally of both the Entente and Central Powers prior to American entry into the war in 1917. American armed forces were not viewed as being on an equal footing as European armies; however, by 1917 the Allies were looking for potential partners regardless of military capacity. America's ability to wage a war outside of its own home waters made it an attractive ally.
The United States, though it possessed its own set of colonies in the Caribbean and Pacific, claimed early after entry into WWI that it did not want any new territory. This allowed Wilson to sell the war to the American people as a moral crusade to save a Europe that was consumed by a need for territorial expansion. In order to make this distinction clear, the United States called itself an "associated power" rather than an "ally" of the Entente.
American entry into WWI was largely due to Germany's unrestricted submarine warfare in early 1917. These attacks against American shipping largely happened in European waters, since most Germany U-boats at that time lacked the range to go elsewhere. American imperial interests were never in real danger during the war, though the Zimmerman note was viewed as an attack on the nation's honor and the Monroe Doctrine. Imperialism played a major role in the European alliances and arms races that took place prior to 1914; however, other than building the American economy and demonstrating that the United States could project power abroad, imperialism had little direct influence on the American decision to join the war in 1917.