Answer: "Preaching against British appeasement of the Japanese" means that someone is giving a speech or expressing their views publicly in opposition to the British policy of appeasing or trying to satisfy the demands of the Japanese. In this context, "preaching" means advocating or promoting a certain viewpoint or idea with passion and conviction.
During the period leading up to World War II, Britain, like many other Western powers, pursued a policy of appeasement towards Japan in an effort to avoid conflict. However, some individuals or groups may have spoken out against this policy, arguing that it was ineffective or even harmful in the long run. "Preaching against British appeasement of the Japanese" would therefore refer to these individuals or groups who were critical of Britain's approach towards Japan.
Explanation: In this context, "preaching against British appeasement of the Japanese" means criticizing or speaking out against the British government's policy of trying to appease or accommodate the Japanese government's aggressive actions, rather than taking a more confrontational stance towards them. The phrase suggests that the State Department had been consistently warning the British government about the dangers of appeasing Japan, and now the British officials were experiencing a similar feeling of betrayal by the Japanese that the Americans had warned them about. The Foreign Office officials are not unhappy to turn the tables on the State Department, perhaps indicating a sense of satisfaction at the American officials now experiencing what the British had experienced before.