Rupert Cornwell: Do mention the Germans, Uncle Sam

What links Fred Astaire, Herbert Hoover, Doris Day, Babe Ruth and Donald Trump? Three more names that could be added to the list – Dwight Eisenhower, Wernher von Braun and Henry Kissinger – surely give the game away. On the other hand, a fourth name, Leonardo DiCaprio, would thoroughly confuse you. But the mystery is resolved by DiCaprio's middle name of Wilhelm. All of the above, from the legendary baseball slugger to the star of Titanic, are, of course, German-Americans.

Often, in recent US history, that particular ancestry has not been much to boast about. The one thing that many Americans know about Germany, even now, is the latter's responsibility for the events recorded at the Holocaust Museum here in Washington DC. But last month a modest counterweight of kinds opened a mile or so away, in the Penn Quarter, the hottest downtown entertainment neighbourhood.

The German-American Heritage Museum does not set out to give an alternative, sanitised history of Germany. It dispels the tiresome myth that in 1794, Congress came within a single vote of declaring German to be the official language of the fledgling United States. But it does demonstrate that the US and Germany are bound together by an umbilical cord.

According to the 2000 census, more than 42 million Americans, 15 per cent of the total, claimed German ancestry – more than the country's entire African-American population, half as many again as self-declared Irish-Americans, and almost double the number tracing their origins to England. Given the bad publicity for Germany over the years, the figure probably understates reality.

Germans were coming here from the very start. A doctor called Johannes Fleischer, was among the first settlers from England to arrive at Jamestown, Virginia, in 1607. Their settlement proper was at a place called (you might have guessed it) Germantown, now part of blighted north Philadelphia but which, in 1688, was home of America's first anti-slave movement. In the centuries that followed, millions joined them. And they have left a mark to match.

We British sometimes imagine America is shaped in our image. In fact, a German played a giant role in ending British rule here. Indeed, if you think America is too obsessed with its undoubtedly top-drawer military – might that not be indirectly due to General Friedrich Wilhelm von Steuben, the Prussian who trained George Washington's Continental Army, turning a rabble into the serious fighting force that won the country's independence?

German-American commanders have led many triumphant US armies since: Generals John Pershing in the First World War, Eisenhower in the second, and Norman Schwarzkopf in the 1991 Gulf War. Just to balance things out, America's most famous military loser, George Custer, was also a German-American. The virtues upon which America has been built, some would say, are those famous "Midwestern" values of common sense, unpretentiousness and unassuming decency. If so, we should also hold Germans largely responsible, given that the region where German-Americans are most strongly represented is that very same Midwest.

One of the most striking aspects of the US is its profusion of community-based interest groups. I would venture this is not unconnected with the tradition of Vereine, of "unions" or clubs, brought with them by German immigrants. Sometimes that sense of community can turn into a bossiness and pressure to conform.

It was a German-American, too, who gave America some of its most potent political imagery. Thomas Nast was born in the Rhineland Palatinate. In 1849, he emigrated to New York, where, as a caricaturist for Harper's Magazine, he produced the definitive depiction of Uncle Sam in top hat, goatee beard and striped trousers,.

But in 1917, America entered the First World War, and the country of Thomas Nast became its mortal enemy. German culture was shunned. Frankfurters turned into all-American hot dogs and sauerkraut was renamed "liberty cabbage". The Second World War made matters even worse for the Germans.

The new museum in Washington is not to everyone's taste. A Washington Post columnist criticised it as another example of the "Balkanisation" of US history, as each ethnic group extols its contribution to the country. But why not? The fascination of this country lies in its diversity. We hear so much about the greatness of America. So why not about the greatness of its constituent parts – of whom none were more numerous than the Americans who came from Germany?