Peace through strength" is a phrase that suggests that military power can help preserve peace. It is quite old and has famously been used by many leaders from Roman Emperor Hadrian in the second century AD to former US President Ronald Reagan in the 1980s.

The concept has long been associated with realpolitik. The idea has critics, with Andrew Bacevich stating, "'Peace through strength' easily enough becomes 'peace through war.'"

The phrase and the concept date to ancient times. Roman Emperor Hadrian (AD 76–138) is said to have sought "peace through strength or, failing that, peace through threat."Hadrian's Wall was a symbol of the policy.

Credits... Wikipedia