In the early 19th century, national consciousness revived in Iceland. The Althingi had been abolished in 1800 but was reestablished in 1843 as a consultative assembly. In 1874, Denmark granted Iceland home rule, which again was extended in 1904. The constitution, written in 1874, was revised in 1903, and a minister for Icelandic affairs, residing in Reykjavik, was made responsible to the Althingi. The Act of Union, a 1918 agreement with Denmark, recognized Iceland as a fully sovereign state united with Denmark under a common king. Iceland established its own flag, but Denmark continued to represent Icelandic foreign affairs and defense interests.

German occupation of Denmark in 1940 severed communications between Iceland and Denmark. Consequently, Iceland moved immediately to assume control over its own territorial waters and foreign affairs. In May 1940, British military forces occupied Iceland. In July 1941, responsibility for Iceland's defense passed to the United States. Following a plebiscite, Iceland formally became an independent republic on June 17, 1944.

In October 1946, the Icelandic and U.S. Governments agreed to terminate U.S. responsibility for the defense of Iceland, but the United States retained certain rights at Keflavik. Iceland became a charter member of the North Atlantic Treaty Organization (NATO) in 1949. After the outbreak of hostilities in Korea in 1950, and pursuant to the request of NATO military authorities, the United States and Iceland agreed that the United States should again be responsible for Iceland's defense. A bilateral defense agreement signed on May 5, 1951, is the authority for U.S. military presence in Iceland. Iceland is the only NATO country with no standing military of its own.