Why England Slept examines why Britain was slow to prepare militarily for the threat posed by Nazi Germany during the 1930s. Kennedy considers the country’s movement from disarmament towards rearmament and argues that its lack of preparedness cannot be explained simply by the decisions of individual political leaders. He instead looks at the pressures created by democratic government, public opinion, economic conditions and uncertainty about the scale and timing of the German threat.

The work gives particular attention to appeasement and the Munich Agreement of 1938. Kennedy does not treat appeasement solely as a failure of leadership, but places it within Britain’s wider political and strategic circumstances. His central argument is that a democracy may require considerable time to build public support for major changes in defence policy. Originally written as his Harvard senior thesis, the study uses Britain’s experience to consider the difficulties democratic states can face when responding to an emerging international threat.