Whenever the Soviet Union conquered a new land, the hard men in charge of security adopted a ruthless policy to prevent rebellion. Rather than wait for unrest to begin, they would murder or deport the kind of people who might be inclined to cause trouble in the future.

The NKVD was instinctively suspicious of educated professionals, such as teachers, doctors or lawyers. Priests were also viewed with profound misgivings, along with anyone who had ever served in the army. The response was ruthlessly simple: people like this would be shot or transported, just in case.

The Soviet invasions of eastern Poland in 1939 and the Baltic states in 1940 were followed by the pre-emptive imprisonment or execution of tens of thousands of people who happened to fall into suspicious categories. When the Soviet Union re-conquered Estonia, Latvia and Lithuania after the Nazi occupation in 1944, the same pitiless procedure was followed all over again.

Today, just about every citizen of these three countries can tell you about an ancestor who was cast into a Siberian gulag or an unmarked grave. You did not actually have to be a dissident to suffer this vengeance – you only had to look as if you might become one.