Above: The Signing of Peace in the Hall of Mirrors, Versailles 1919, by William Orpen
The answer to the first question is easy: of course. The U.S. could easily have avoided the war, if it chose to. That brings up the second question: why did the U.S. choose to enter the war, and did it matter? This is somewhat more complicated.
The first reaction might be, so what? That means that history is irrelevant. Well, then, what is relevant? Did World War I have any consequences for this country, for the world? The answer, just about everything: World War II, Hitler, Lenin, Stalin, the Cold War, NATO, Korean, Vietnam Wars, the end of colonialism, Israel, the rise of the Middle East, Islam, and the current war on terror (to mention a few).
To assess the consequences of the question, history needs to be re-examined. When the war began in 1914, President Woodrow Wilson immediately declared U.S. neutrality. In 1916, he won another term with the slogan “He Kept Us Out of War.” Five months later, he declared war on Germany; Congress approved with 56 “No” votes. Were the opponents right? What happened?
Background will tell us something. How “neutral” was the U.S.? First, all the Cabinet members, except one, plus Wilson, were fervently pro-British. The exception was Secretary of State William Jennings Bryan, who resigned in protest in 1915. Second, the moment war began, the American industrial and financial system, then in a depression, began pouring arms, munitions, and bank loans to the Allies (primarily Britain and France). At the same time, the British Navy began a tight blockade of the Central Powers (Germany, Austria-Hungary), thus restricting any possibility of trade or aid getting through.
The blockade was so tight that trade with Germany fell to almost nothing by the middle of the war. In 1914, U.S. trade with Germany totaled 170 million dollars; by 1917 it had dropped to about one million, a 99.9% decline. Trade with the Allies in 1914 was about 825 million dollars; in 1917, it had risen to about three trillion, a 300% increase.
Beyond the blockade of the continent, Britain mined the North Sea, thus supervising all American cargo ships that needed sailing instructions. If the cargo was objectionable, the ship was seized and brought to a British port. The British Navy ruled the entire ocean. American merchant ships suspected of carrying contraband were seized, often boarded, and often brought to ports and held for periods of days or weeks. Official Washington sent diplomatic protest notes to the British Foreign Office, but they were either ignored or delayed for months at a time. Interior Secretary Franklin K. Lane summarized the U.S. attitude:
“There isn’t a man in the Cabinet who has a drop of German blood in his veins, I guess. Two of us were born under the British flag. I have two cousins in the British army, and Mrs. Lane has three. …Yet each day that we meet we boil over somewhat, at the foolish manner in which England acts. Can it be that she is trying to take advantage of the war to hamper our trade?”
The U.S. Ambassador, Walter Hines Page, was more pro-British than American. Historian Thomas A. Bailey wrote, “Instead of faithfully representing the United States in England, as was his duty, Page represented the British cause to the government in Washington. His bias finally became so blatant that President Wilson wrote him off as ‘really an Englishman.'”
British behavior on the high seas was flagrantly illegal. In January 1917, Germany announced a resumption of “unlimited” submarine warfare, which was also illegal. In March, German subs began sinking unarmed American merchantmen, and, in April, the U.S. declared war. The world hasn’t been the same since.
In order to assess the original question, we have to change the U.S. position entirely. President Donald Trump has been accused of lying, but politicians have been known to lie. Still, of all the presidential lies in American history, none may equate with the fabrication of American “neutrality” in World War I. In criminal cases, to “aid and abet” is to be liable. U.S. aid/trade kept the Allies afloat until American soldiers won the war (in six months).
But what if the U.S. had authentically stayed neutral? How would the century have unfolded? First, some sort of “Cold War” would have occurred anyway. The Bolsheviks declared war on the capitalist world in their 1917 revolution, and the U.S. was capitalist.
Second, the most that can be stated with confidence is that World War II could/should have been avoided. By 1918, after four years, both sides were exhausted and war-weary. There was mutiny in France, impatience in England, and revolution in Germany. The end was in sight. It would have been a negotiated armistice or a German victory. The Allies alone could not possibly have defeated Germany.
Without U.S. entry, there would have no Versailles Treaty, termed a “diktat” by Hitler, who used it to arouse Germany against the Weimar Republic and Wilson’s League of Nations. Neither the U.S. nor Germany (nor Russia) joined the League initially, and the U.S. never joined. Both Weimar and the League became two of history’s worst creations; both collapsed and made the Second World War a near certainty. Wilson’s acquiescence to French demands for an occupation, reparations, and German acceptance of war guilt made the next war absolutely certain.
The other events of the century would have mostly still occurred, with time and circumstance different: the end of colonialism, birth of Israel, Communist China, Cold War, Islamic terrorism.
Should the U.S. still have stayed out? Only if you wanted to avoid World War II, the worst man-made calamity in history.
On the Versailles Treaty, French Marshall Foch stated, “This is not peace. It is an armistice for 20 years.” As Prime Minister, Churchill wrote President Roosevelt that the Second World War was “The unnecessary war, there never was a war more easy to stop.”
From hindsight, neither man knew how right he was.