Perhaps the most valid justification of government is its defense of citizens against foreign aggressors. But when governments wage war, a thin line separates defense and offense. And even in a defensive war, governments typically deprive their own citizens of many liberties. Historically, war has done more than anything else to enhance the power of governments and to diminish the liberties of the people. Classical liberals have always recognized the dangers of war and supported policies, such as free international trade, that reduce the likelihood of war.