the British waited to release the Zimmermann telegram to the US because they wanted to make sure would have a significant impact on US public opinion and encourage them to join the war One piece of evidence supporting this is the fact that the news of the telegram was "splashed across the front page of American," indicating that it was meant to be widely publicized to garner attention. Another piece of evidence is the timing of the US declaration of war on Germany just one week after the news broke, suggesting that the British strategically waited for the right moment to reveal the telegram. This shows that the British were strategic in their decision to release the information when they believed it would have the most impact on US involvement in the war. i hope this really helps