Another Kantian argument is that democratic decision making faces procedural hurdles and the need to enlist popular support, delaying decisions on both sides when democracies are in conflict and leaving time for peaceful resolution. But sometimes popular support is there already, sometimes the problem facing leaders is not to enlist it but to resist it, and often enough they have manufactured it with remarkable alacrity. Besides, democracies today have semimobilized standing forces with executive authority to use them. Hockey teams have norms for peacefully settling internal conflicts, but externally they compete as ruthlessly as possible. So do corporations and armies.
All durable states enjoy internal peace, but the democratic ones foster competition for power.
Alexander Hamilton was not naive about popular passions. He knew that majorities could be as belligerent as monarchs. Assuming lax enough tests of democracy, exceptions to democratic pacifism abound. With limited suffrage but the mother of parliaments, Britain fought the United States in 1776 and 1812 and revolutionary France in its comparatively democratic years of 1793 and 1795. In the American Civil War, North and South shared a democratic history of fourscore and several years.