Which still begs the question of why the UK and the US entered the European war at all.
Germany and Italy were seeking territorial expansion into Eastern Europe and North Africa (the latter because of the oil reserves there). If Germany was to dominate mainland Europe it was also necessary to deal with France. They offered little or no threat to either British or US interests. British interests centred on India, Southern Africa, the Caribbean, South-East Asia, Australasia and Canada. US interests were in South America and those parts of South-East Asia and the Pacific Rim not already controlled by the British Empire.
Thus Japanese expansionism posed a threat to both UK and US interests, and an alliance against Japan would have made sense, and made the war much shorter and easier for both of us. It was the entanglement in Europe that proved so costly, and at no time was it necessary for either of us.
Hitler did not wish to engage with the British Empire, and indeed made every effort to secure a committment from us to stay out of Europe. To this day I canot see a single valid reason for Britain to have entered either the Great War or the Second World War.