The First World War leaves a bad taste in everyone’s mouth. The casualties in every army were appalling, the economic damage colossal and the peacemaking a master class in how not to terminate a war.

“Never Again!” Americans said at the time, which explained the spread of isolationism and protectionism in the interwar period and the ambiguity ever since about what the war actually achieved.

And yet 1918 was the year that the United States became what it has been ever since: the greatest of the great powers. But it was also the year that failures in American leadership, combined with a partisan media, undermined Washington’s international position, paving the way for the Second World War.

A century ago, decision-makers in Berlin grasped that American entrance into the war was the beginning of the end for them. Capable of beating Britain and France — Germany nearly did in the spring and summer of 1918 — the Germans understood that they would never beat the United States.

They circulated a report that contained some harsh facts: by the autumn of 1918, with German, British and French manpower exhausted, the Americans had 1.5 million troops in France, two million more in training, and 14 million men registered and available for military service. The United States, the Germans noted, was spending $50 million a day — $1 billion a day in today’s dollars.

In just its first year of war, Washington had spent more than London had spent in its previous three years of war, and the United States was feeding itself and exporting $1.4 billion worth of food — $28 billion today — every year to the hungry Allies.

American industry was also furnishing the bulk of the aircraft on the Western Front — 1,500 planes a month — and had become the world’s greatest shipbuilder, transporting 300,000 troops a month to France. Britannia still ruled the waves, but not for long. In 1918, the British needed five years to build what American shipyards could build in just one.

The US Army did not delay in ramming home the truth of the report, destroying the Germans on the battlefield in 1918. The Russians had surrendered, the Italians had all but dropped out of the war and the British army, victimised by massive casualties, lacked the reserves to battle across the Rhine or even clear the Germans out of France and Belgium. The French army, which had mutinied against its officers in 1917 and nearly collapsed again in June 1918, was physically incapable of freeing German-occupied France and Belgium.

To defeat Germany on the battlefield, the Americans suffered appalling casualties — the highest monthly rate in US history, six times higher than during the Second World War. But they seized the “vital pivot” of the German army in France and Belgium: the four-tracked railway centre at Sedan. This denied the Germans on the Western Front more than half of their troop-and-supply moving capacity, and breached the barrier of the Meuse River.

Unable to move, unprotected by the Meuse, the three million-strong German army surrendered, stating bluntly that it had been American intervention that compelled the surrender. At best, the French and British would have battled to a stalemate; at worst, they would have been defeated.

And yet for all of this American might, the peacemaking process failed miserably. Why? Chiefly because of poor American leadership.

Newer analyses of the Treaty of Versailles make the point that the peace was not nearly as hard on Germany as critics ranging from Adolf Hitler to John Maynard Keynes contended. In fact, German inflation erased the massive German war debts, and the collapse of the Russian and Austrian empires meant that Germany gained new influence over weak, dependent or merely vulnerable states such as Hungary, Romania, Poland and Czechoslovakia. Absent Hitler, Germany would have recovered to dominate and prosper in this space no less than it does today.

And it was the reckless American retreat from global responsibility after 1918 that propelled Hitler into power. A century ago — no less than today — Washington wrestled with a president convinced that he had a knack for disrupting global power relations. This grandiose conceit produced executive grandstanding exacerbated by partisan politics and an impassioned media.

Woodrow Wilson, having overcome the United States’ gross military unpreparedness in 1917 to secure a great victory, had a golden opportunity to crown the American triumph in 1918 with new security arrangements that would ensure the peace. He actually negotiated a Treaty of Guarantee in Paris that would have allied the United States with Britain and France to guarantee the French-German border against future German aggression. The Senate might well have ratified both that treaty and the Treaty of Versailles.

But Wilson insisted on combining them with the League of Nations Covenant. The covenant was unconstitutional, in that it transferred war powers from the US Senate to the League of Nations. It was also politically controversial.

Republicans, in control of Congress after the 1918 midterm elections, were eager to pass the Treaty of Versailles and might have been persuaded to ratify the Treaty of Guarantee. But they refused to go along with Wilson’s “rainbow chasing”. When Wilson, with stunning hauteur, insisted that the Republicans “take their medicine” and submit to the League of Nations as “the organised moral force of men throughout the world”, they resisted.

Senator Henry Cabot Lodge’s Foreign Relations Committee accepted Wilson’s treaties with 14 “reservations” that restored US national security decision-making to Washington — “America must be master of her fate,” Lodge insisted — but Wilson refused even to consider the Republican amendments. He called Lodge’s reservations “a knife thrust at the heart of the treaty”.

The media joined the fracas, with Democratic papers calling Lodge’s Republicans “the Hindenburg Line in the Senate”, and Republican papers decrying Wilson’s “immeasurable vanity and ambitions”.

White House leaks featured in the drama, too, with someone revealing that Wilson’s own secretary of state had declared privately that the League of Nations was an abstraction in need of killing. Wilson refused to convert the League idea into a focused mechanism for the application of economic sanctions and international law, and so the Treaty of Versailles languished.

This failure prompted the United States to veer into isolationism, determined not, as Lodge put it, “to be entangled in the intrigues of Europe”.

Ultimately, none of this political drama prevented the United States from becoming the greatest of the great powers, as its economic and military rescue of the faltering Allies in the Second World War demonstrated so vividly. Washington would be caught again, as the French put it, “in flagrante delicto of military unpreparedness”, but would marshal the necessary resources and apply the methods of 1918 to land on hostile shores, destroy fascism and then take up the work of containing communism.

The First World War engineered a reordering of world power that persists to this day. But the cautionary tale of 1918 is highly relevant today. Even the strongest power can be paralysed by partisan infighting, media wars and a failure by both parties to work effectively towards a national security consensus that upholds American power, independence and values.

• Geoffrey Wawro is professor of history and director of the Military History Centre at the University of North Texas, and author of Sons of Freedom: The Forgotten American Soldiers Who Defeated Germany in World War One