The reality of the situation, unlike what is trying to be portrayed here, is that the United States had a mixed interest in the 1st World War. Unlike Canada, which is largely (but not entirely) British and French descendants, the United States had a much more mixed population, from every European nation, large numbers of German and Austrian immigrants had arrived in the States in the last 30 years. Wilson was concerned, that declaring for one side or the other would immediately cause a civil war or, at the very least, massive riots within the country itself. Wilson knew that he couldn't just pick a side, even though he favored involvement on the Allies side, there were many people even within his administration that favored the Central Powers. All the sensationalizing, which was all it was, couldn't convince enough people to pick a side, it was "Over There." Something had to happen that directly affected the people of the United States for Wilson to be able to make a declaration without causing the internal strife that would have rendered any aid that the US could have provided, useless. The United States involvement in WWI was minimal, almost non-existant, except that it allowed the Allied Commanders to spread out the French troops, who had already surrendered, (They would no longer attack, they would defend themselves, but they would not launch ANY offensive operations) and replace them with US soldiers, who, while they had heard of Mustard Gas, Flamethrowers, etc... hadn't seen them first hand, yet, and thus were willing to (at this point) "Save the Democratic World!". Had the US tried to get involved prior to the (fabricated) Zimmerman Telegram, the small amount of forces that would have been able to be raised, would have immediately been tied up trying to suppress German and Austrian Nationals that would have risen up against the involvement.
At the end of World War I, Wilson had wanted a "peace without victory" but given the US's minimal involvement, and France's burning desire for revenge, Wilson's desires were ignored. (Rightly from the perspective of their limited involvement, but wrongly from what France ultimately wanted to do) But after watching the lengths that France (and Britain) went to to "punish Germany" who was merely helping their ally to begin with, the United States realized the wisdom of a President from 100 years prior, James Monroe. European Affairs were for Europeans to deal with. At the onset of World War II, the US was even more determined to sit on the sidelines, even though the Japanese actions in China was already pushing Roosevelt to intervene there (the US had cut off Oil Exports to Japan in the Summer of 1941, the US at the time was the world's leading Oil producer). I think without Pearl Harbor, the United States would have joined the war in the following spring, simply because of the skill of the German War Machine, and that there was actually evidence of the atrocities that was being committed by the Nazi forces, rather than the unsubstantiated hearsay that was being spread during WWI about the "Barbaric" Huns.