Military service Clark had been a member of the
Officers' Training Corps attached to the
University of Oxford during his studies. On 26 August 1914, he was
commissioned into the
Post Office Rifles,
British Army, as a
second lieutenant. On 27 May 1915, he was promoted to
lieutenant. During the early part of
World War I, he was wounded twice. At the time of his capture, he held the rank of
captain. He was held in
Gütersloh and
Krefeld, and spent his time learning languages. He was released at the end of hostilities and returned to Britain. Between the 1930s and 1960s, Clark was the editor overseeing the
Oxford History of England series and wrote Volume X:
The Later Stuarts, 1660–1714 (1934), which was the first of the series to be published. His
The Seventeenth Century appeared in 1929, and he wrote numerous other monographs. He was twice editor of the
English Historical Review. Clark delivered the Wiles Lectures in the Queen's University of Belfast in October 1956. They were published as
War and Society in the Seventeenth Century (Cambridge UP, 1958). ==Honours==