Answer: "Raised the matter" means to bring up a particular subject or topic for discussion or consideration. It typically involves initiating a conversation or drawing attention to a specific issue or concern that may require further attention or action.
Explanation: "Raised the matter" in this context means to bring up a particular issue or topic for discussion or clarification. The passage describes how Lord Halifax, the British Ambassador, complained to Hull on May 24, after having raised the matter with Welles the previous day. The matter being discussed is a private initiative to adjust Japanese-American relations, which had been reported in the American press and was inquired about by the Canadian government. Therefore, in this context, "raised the matter" means to bring up the topic of the private initiative and express concern or dissatisfaction about it.