When U.S. President Donald Trump last spoke with Prime Minister Justin Trudeau, Trump pointed to a 1908 treaty as apparent ammunition to support his threats of a tariff war and his envisioned takeover of Canada.

Trump's reference to the 116-year-old treaty regarding the Canada-U.S. border reportedly took Trudeau and his office by surprise, sending staff searching for the pact online as the leaders spoke on the phone. That's not a surprise. The treaty is somewhat obscure in terms of the historical relationship between the former British colonies that became Canada and the United States of America.