In Canada, the Canadian Armed Forces (CAF) are responsible for external security; the CAF’s core missions include detecting, deterring, and defending against threats to or attacks on Canada; the military also provides assistance to civil authorities and law enforcement as needed for such missions as counterterrorism, search and rescue, and responding to natural disasters or other major emergencies; it regularly participates in bilateral and multinational training exercises with a variety of partners, including NATO (Canada is one of the original members) and the US; the CAF also contributes to international peacekeeping, stability, humanitarian, combat, and capacity building operations, principally through NATO, but also with the UN and other security partners

Canada is part of the North American Aerospace Defense Command (NORAD; established 1958); NORAD is a Canada/US bi-national military command responsible for monitoring and defending North American airspace; traditionally, a CAF officer has served as the deputy commander of NORAD; Canada’s defense relationship with the US extends back to the Ogdensburg Declaration of 1940, when the two countries formally agreed on military cooperation, including the establishment of the Permanent Joint Board on Defense (PJBD), which continues to be the highest-level bilateral defense forum between Canada and the US

British troops withdrew from Canada in 1871 as part of the US-UK Treaty of Washington; following the withdrawal, the first Canadian militia, known as the Royal Canadian Regiment, was organized in 1883 to protect Canadian territory and defend British interests abroad, which it did in the South African War (1899-1902), Canada’s first overseas conflict; militia units formed the backbone of the more than 425,000 Canadian soldiers that went to Europe during World War I in what was called the Canadian Expeditionary Force; the Royal Canadian Navy was created in 1910, while the Canadian Air Force was established in 1920 and became the Royal Canadian Air Force in 1924; the Canadian Army was officially founded in 1942; a unified Canadian Armed Forces was created in 1968 (2025)