Why defence needs matter more than a GDP percentage

What percentage of GDP should a country spend on defence in peace and war?

There is no universal percentage: countries should fund the forces their threats and commitments require, using GDP targets only as rough political shorthand.

Wartime spending must respond to the conflict being fought. In peace, a universal percentage can encourage unsuitable purchases or broaden the accounting categories used to reach a headline target. Ireland's proximity to Britain and NATO, and Canada's relationship with the United States, illustrate how geography and neighbouring powers affect national defence needs. Spending should therefore follow an assessment of security requirements, supported by both short- and long-term plans. The recommendation for Britain to spend more than three percent is a political argument for increasing funding, with explicit acknowledgement that the percentage is a poor substitute for that assessment.