Until recently, the international border between Canada and the U.S. was frequently referred to as the world‘s longest ‗unguarded‘ or ‗friendly‘ border. While the border was never truly left unguarded, Canadian and U.S. citizens enjoyed relatively open borders, without the enforcement of passport requirements. On September 11, 2001, the porous border that had symbolized international cooperation, friendship and the world‘s largest bilateral trade relationship, was abruptly re-defined in the public eye as a potential liability in the U.S. national defense system.
Vance, Anneliese, "Crossing Bridges: Observations and Strategies by Cross-Border Business Communities in an Evolving Regulatory Environment" (2012). Border Policy Research Institute Publications. 71.