"The nexus among border control, illegal immigration, homeland security, and other transnational criminal activity has been a subject of much debate in the past especially since the terrorist attacks of September 11, 2001. Because much of the immigrant population residing in the United States illegally is believed to be from Mexico, Central, and South America the focus on the border between the United States and Mexico is logical. However, the border between the United States and Canada is the largest land border between nations and represents almost 4,000 miles of poorly controlled territory and is more than twice the size of the boundary shared with Mexico. The threat is greater than the seam created by the boundary or the geography. More important, perhaps, is the potentially explosive nature of the environment created by the confluence of a myriad of issues. Concerns like the mature lines of communication (LOCs) used for trafficking and smuggling between the ports of entry (POEs), a focus on cross border economic flow at entry points, and a growing number of Syrian refugees in Canada, all come together and combine with the geography to create significant security concerns."
Defense Technical Information Center (DTIC): http://www.dtic.mil/dtic/