To American perceptions shortly before World War One, the history of the French promotion of Emperor Maximilian 50 years earlier formed a background to the especially strong hostility to Germany's plan to 'allow' Mexico to annex formerly Mexican lands in the Southwestern US.
When the British intelligence service, therefore, leaked the contents of the Zimmermann Telegram, containing the German plan, to the US authorities, it knew that US reaction would be hugely angry and hostile. It was thus judged worthwhile to fake a robbery where the British supposedly 'discovered' the Zimmermann Telegram, and then they 'helpfully' showed it to the US mission in London, thus avoiding the implication that the British had been reading the coded communications to Washington, DC., but currying favor with the US, whose assistance as an ally in World War One was strongly desired.
The British intelligence service thus reckoned correctly that, just as the US resented French promotion of Emperor Maximilian of Mexico during the American Civil War, as a European interference in Western Hemispheric affairs, so also the US, with memories of the sinking of the Lusitania, would also hugely resent the Zimmermann Telegram.
There is thus an undoubted historical and geopolitical link between Mexican Emperor Maximilian's short reign and the events 50 years later which led to the US entering World War One on the side of the British, the French, and the Italians.
In the event, Mexican President Don Feliciano Carranza, rejected the contents of the Zimmermann Telegram's proposals, but it was deemed somewhat irrelevant in the US in any case: the US had already declared war on Germany.
(Read: 'Venustiano Carranza')