The British waited to ensure the Zimmerman Telegram would prompt US entry into the war by revealing its threat and intensifying public opinion against Germany.
The British waited until they were sure the telegram would encourage the US to enter the war for several reasons. Firstly, the intercepted Zimmerman Telegram contained a direct threat on American soil, increasing public opinion against Germany. Secondly, the British intercepted and shared the decrypted message with the US public, intensifying anti-German sentiments and pushing for US intervention in the war.
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