Columbia subject headings:
Border patrols--Northern boundary of the United States.
Canada--Relations--United States.
Drug traffic--Northern boundary of the United States.
Illegal immigration--Northern boundary of the United States.
Noncitizens--Northern boundary of the United States.
United States--Relations--Canada.
Harvard subject headings:
Border patrols--Northern boundary of the United States.
Drug traffic--Northern boundary of the United States.
Illegal immigration--Northern boundary of the United States.
Noncitizens--Northern boundary of the United States.
Terrorism--Canada.
Terrorism--United States
Princeton subject headings:
Border patrols--Northern boundary of the United States.
Canada--Relations--United States.
Drug traffic--Northern boundary of the United States.
Illegal aliens--Northern boundary of the United States.
United States--Relations--Canada.