Homeland defense is a basic function of our government, and has been since the colonial era. Over 100 years before our Constitution established as a fundamental responsibility of government to "provide for the common defense," American colonial leaders recognized the need for a homeland defense capability and established colonial militias to fight both internal and external threats. As the U.S. grew in economic and political power, our homeland defense needs changed, as well. By the 20th century, homeland defense encompassed not only defense of U.S. territory and population, but overseas possessions, access to critical lines of communication, natural resources, and trade. The Cold War again qualitatively and quantitatively changed the concept of homeland defense.