Answer: "The old refrain" is an idiomatic expression that refers to a repeated or familiar theme or idea, particularly one that has been expressed or heard many times before. The phrase can be used to describe something that is becoming predictable or monotonous due to its repetition. It is often used in a negative context, to suggest that something is becoming boring or tiresome because it has been said or done so many times before. The phrase can be applied to a wide range of contexts, including music, literature, art, politics, and everyday conversation.
Explanation: In this context, "the old refrain" refers to a well-known nursery rhyme or children's song that goes, "Leg over, leg over, the dog went to Dover." The phrase is being used somewhat ironically to describe the German invasion of Crete, as if the military campaign is following a familiar and predictable pattern, like a children's song that is sung over and over again. The author is suggesting that the invasion is part of a larger, repetitive pattern of aggression and conflict that has characterized European history for centuries. The phrase "the old refrain" is also being used to create a sense of contrast or irony, as the violent and deadly events being described stand in stark contrast to the innocent and harmless nature of the nursery rhyme.