Lord Guthrie joined the British Army in 1959, when Britain’s influence was shrinking around the world, and he left in 2001 when that influence was once again expanding. Throughout his career he has served in Aden, Northern Ireland, Cyprus, Kenya, Germany, UK and the New Hebrides. As a senior officer, he was General Officer Commanding 1st British Corps when the Soviet Union collapsed and the Cold War ended. Subsequently, he was instrumental in bringing Eastern European countries into NATO as part of Partnership for Peace. When Chief of the General Staff He was closely involved in the Northern Ireland peace process, as well as being responsible for the British Army's involvement in the UN and NATO operations in Bosnia, and as Chief of the Defence Staff he oversaw Britain's military role in the wars in Kosovo and Sierra Leone. He oversaw the modernization of the Army following the Cold War years and shaped the way the Army operated, updating doctrine from the plains of North Germany and the streets of Northern Ireland to the conflicts in the Balkans and Sierra Leone. He retired from the Army as Chief of Defence Staff in 2001, before the Iraq and Afghanistan wars.