United States
In a reaction to the bombing of Pearl Harbor by Japan in 1941, United States Executive Order 9066 on February 19, 1942 allowed military commanders to designate areas "from which any or all persons may be excluded." Under this order all Japanese and Americans of Japanese ancestry were removed from Western coastal regions to guarded camps in Oregon, Washington, and Arizona, Germans and Italians were removed from the East Coast, and roughly 1/3 of the US was declared an exclusionary zone.
Almost 120,000 Japanese Americans and resident Japanese aliens would eventually be removed from their homes as part of the single largest forced relocation in U.S. history.
See Japanese internment in the United States.
Britain
During World War II, about 8,000 people were interned in Britain. They included enemy aliens, refugees who had fled from Germany, and British Nazi sympathisers. Initially they were shipped overseas, but that was halted when a German U boat sank the SS Arandora Star in July 1940 with the loss of 800 internees, though this was not the first loss that had occurred. The last internees were released late in 1945, though many were released in 1942. In Britain, internees were housed in camps and prisons. Some camps had tents rather than buildings with internees sleeping directly on the ground. Men and women were separated and most contact with the outside world was denied. A number of prominent Britons including writer H. G. Wells campaigned against the internment of refugees.
Initially the British government rounded up 74,000 German and Austrian aliens, but within 6 months the 112 alien tribunals had individually summoned and examined 64,000 aliens, designated them as "friendly aliens" and freed them from internment with no special restrictions, eventually only 2,000 of the remainder were interned.
Overseas, British citizens were also interned by the Axis powers.
Northern Ireland
One of most famous example of modern internment and one which made world headlines occurred in Northern Ireland in 1971, when hundreds of nationalists and republicans were arrested by the British Army and the Royal Ulster Constabulary, on the orders of then then Prime Minister of Northern Ireland, Brian Faulkner. Historians generally view that period of internment as inflaming sectarian tensions in Northern Ireland while failing in its stated aim of arresting members of the paramilitary Provisional IRA because many of the people arrested were completely unconnected with that organisation, but had had their names appear on the list of those to be interned through bungling and incompetence. The backlash against internment and its bungled application contributed to the decision of the British government under Prime Minister Edward Heath to suspend the Stormont governmental system in Northern Ireland and replace it with direct rule from London, under the authority of a British Secretary of State for Northern Ireland.
Many of those interned, were held in a prison called Long Kesh, later known as the Maze Prison outside Belfast.
The republican song The Men Behind the Wire was composed in response to the imposition of internment without trial in Northern Ireland.