For many years, crossing the Canadian/American border was hardly more difficult than crossing from one state to another. In the “good old days,” all you had to do was verbally declare your citizenship at the border and you were good to go. The Western Hemisphere Travel Initiative (WHTI) put an end to that practice.
Under the WHTI, Passengers on US/Canada flights have been required to carry passports since 2007, but the rules remained more relaxed for land and sea crossings.
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