In 1917, America made its first decisive intervention in Europe—a hundred years later, is it about to leave?

Angela Merkel and Donald Trump are clearly not a match made in heaven. After an awkward first encounter when the Chancellor visited the newly installed President at the White House, relations reached a new low at the recent NATO and G7 summits. Acting entirely in character, a combative Trump demanded more defence spending from NATO’s European members and refused to recommit to the Paris climate accords. And acting entirely out of character, the

Acting entirely in character, a combative Trump demanded more defence spending from NATO’s European members and refused to recommit to the Paris climate accords. And acting entirely out of character, the normally-cautious Merkel has responded that Europe can no longer rely on America. The continent, she says, must become responsible for its own destiny. For a leader used to making policy—especially foreign policy—in cautious incremental

For a leader used to making policy—especially foreign policy—in cautious incremental steps, this is a big leap, and one which contains the possibility of a complete re-drawing of Western security architecture.

Meanwhile, in an irony apparently lost on both leaders, America has recently marked the centenary of its commitment to Europe. There were a number of proximate causes for American entry into the First World War, but what began in 1917 still endures in 2017. For the moment, the USA remains the ultimate guarantor of European security.

At the tactical level (where battles are won), the US contribution in the First World War was too little, too late. Even though nearly five million US citizens were mobilized, American arms had only a marginal effect on the battlefields of 1917/18. However, at the strategic level (where wars are won), US impact was decisive.

Before America’s entry, the German armies in the West occupied the most advantageous position available in war—simultaneously on the strategic offensive and the tactical defensive.

Strategically, they occupied large tracts of French and Belgian territory that contained much of those countries’ natural resources and industrial capacity. Tactically, they had constructed formidable defences against which the allied armies dashed themselves in successive failed offensives. It was a position from which they expected to win, or at least negotiate a peace on the very best terms.

All that changed with America’s arrival. US manpower and resources meant the advantage moved ineluctably in the Allies’ favour. The Germans had to renounce tactical defence and risk a winner-takes-all battle before American strength became decisive.

The result was the Kaiserschlact (Kaiser’s battle), launched on 21st March 1918; the 78,000 killed and wounded on both sides made it the bloodiest single day of a very bloody war. After initial success, the Germans ran out of steam, and, after the Battle of Amiens on 8th August, their defeat became inevitable.

The immediate causes were the leadership of Marshal Foch and the relentless pressure of, particularly, the British and Dominion armies. But underneath was the change in the terms of strategic engagement that only America could bring.

In the Second World War, US intervention was decisive at both tactical and strategic levels. In an act of hubris, Hitler declared war on America in the wake of the Japanese attack on Pearl Harbour in December 1941 and so invited the application of overwhelming US military and industrial capacity against German forces already fighting on two fronts.

In a remarkably brave and prescient act, President Roosevelt gave Europe strategic priority over Japan, recognizing that post war global security would owe more to the state of Europe and Soviet strategic ambition than events in the Western Pacific. Under General Eisenhower as supreme allied commander and with Lieutenant General Patton setting the pace, the invasion of Europe on D Day was only possible because of American involvement.

Had the British fought alone in the West, Churchill would never have contemplated D Day and would have played a waiting game by fixing German armies in France while the Red Army eviscerated them in the East. The result would have been a Soviet imperium at the heart of Europe and quite possibly reaching the Atlantic seaboard.

In the event, Europe was divided by what became known as the Iron Curtain and a permanent US presence was institutionalized in peacetime. The Cold War that followed entirely depended upon America, and, if the eventual collapse of the Soviet Union had a single cause, it was the application of US power in Europe.

So, what is happening now is not simply a passing spat between the German and US leaders but the possible termination of a strategic odyssey that America embarked on a century ago. And not just a strategic odyssey, but, perhaps a moral one too. Europe authored many of the abominations of the 20th century from the Holocaust to the Gulag and was redeemed by not only the material energy but also the moral purpose of America.

Is that legacy really at risk from a German politician on the electoral stump and an American politician who cannot miss an opportunity to grandstand? If so, they are unworthy of the history of which they are temporary custodians.