This book examines U.S.-Canadian border threats and defenses and compares the U.S.-Canadian situation with the European Schengen Convention (SC). The Department of Homeland Security coordinates U.S. security with representatives from law enforcement, military and civilian entities. Public Safety Canada coordinates defense in Canada. Prior to the 9/11 attack, the U.S.-Canadian relationship was similar to the SC, focusing on securing external borders while opening shared borders. Some experts, especially in the U.S., argue that border security needs to be tightened further while others contend increased U.S.-Canadian border security is unnecessary and harms commerce. In 2011, Denmark decided to increase internal border security, rejecting the SC tenets requiring common security of external border of the larger Schengen area and open internal zones. The increase represented a case study of unilateral border relations. Although never completed, the lessons of this brief experiment in increased border security are that homeland security decisions are based more on arguments of sovereignty and politics, rather than on objective determinations of threats and security. More broadly, this thesis argues that the U.S. and Canada can benefit from returning to an open border and push the threat as far away as possible.