After Iran, It's Turkey

One puzzle historians have to grapple with is the causality of the Second World War and the timing of British involvement. Britain had far stronger commitments to Denmark in 1864, or Belgium in 1914, than it had with Poland in 1939. Czechoslovakia was a liberal democratic power, much closely aligned with Britain, than a reactionary Catholic Poland with increasing ethnic enmity with both Germany and Russia. Yet it wasn't the collapse of Prague that prompted Britain to join the war, but the attack on Poland. Realist theories of course explain this paradox. After Poland, there was only one balancer state left in the continent, France. Defending France was therefore paramount to British interests. Similar logic predicated in America's involvement, as the collapse of the British empire would have meant Nazi Germany controlling Canada, an unthinkable proposition for Washington (which was, by the way, prompted to take control of Greenland even before an official entry to the war).