It was revised a year later by his successors, Prime Ministers Liz Truss and Rishi Sunak, in response to the Russian invasion of Ukraine.
In response, an emergency summit for European leaders was held in Paris and concluded with an agreement that Europe must do more to defend itself and Ukraine, including through increased defence spending.
The review is to be headed by three external reviewers: Former NATO Secretary General and Defence Secretary Lord Robertson, United States Presidential advisor and foreign policy expert Dr Fiona Hill, and former Deputy Chief of the Defence Staff General Sir Richard Barrons.
They will be supported by a review team comprising experts from inside and outside of government, including those in the armed forces, veterans, the defence industry, the general public, academia, parliament and close allies.
[1] The review is expected to focus on several key areas, including homeland security, support for Ukraine, modernisation of the armed forces, the nuclear deterrent and the UK's continued leadership in NATO.