In 1916, a US amendment was proposed to put all acts of war to a national vote. If you voted yes you would have to register as a volunteer for service in the United States Army.
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The Canadian province of New Brunswick (which was part of the UK at the time) had a bloodless war with the US state of Maine in 1839
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The handbook issued to US soldiers in Britain during WW2 included the line "The British don't know how to make a good cup of coffee. You don't know how to make a good cup of tea. It's an even swap."
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In 1918, a homing pigeon saved over 190 American soldiers by delivering a message to nearby support despite having been shot through the breast, blinded in one eye, covered in blood, and with a leg hanging on by just a tendon.
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