Carl Siemens, chair of Siemens the German electronics business, complained in 1929, ‘the whole world belongs to the Americans.’ If you want to understand how it was that American businesses ended up investing so heavily in Germany in the 1920s and 30s – so heavily that eventually they enabled Hitler to arm the fascist Third Reich - then you have to start by going back to the First World War. It starts with asking why the Americans declared war on Germany on 6 April 1917 but mysteriously did not ally with either Britain or France.