
When I was an undergraduate at Oxford, many years ago, my tutor for 20th-century European history, Martin Gilbert – who was about to become Churchill’s official biographer – set me a question that I found unexpectedly difficult to answer. Why, he asked, did Britain go to war in 1939 to save Poland, a country under an anti-Semitic, authoritarian and aggressively military regime; a country, moreover, whose obsolete military equipment and open northern and western borders on the plains of central Europe made it very difficult to defend? Why Poland when Britain did not go to war the year before to save Czechoslovakia, a liberal, democratic state with modern, well-equipped armed forces and (as he pointed out, showing me one of the maps of which he was so fond) an easily defensible mountainous border with Germany?
What made the question difficult was not really the comparison. It wasn’t hard to conclude that foreign policy was, then as now, about national interest as seen by the government of the day and not about morality. It was clear from the documents Martin set me to read that public opinion in Britain in 1938 was vehemently opposed to war, making it impossible for the government to declare one. By September 1939 it was equally clear that British public opinion had swung round decisively in favour of a war with Germany, making it hard, to say the least, for the government not to.