Liberalism posits that liberty, equality, rule of law and individual rights are the best panacea for ensuring peace in human affairs and a liberal democracy is the best form of government that ensures maintenance of such peace. Liberal approach holds that peace, stability and security are endangered by non-liberal states and that such non-liberal states must be countered.
Thus it was Britain before First World War that strove to take measures to defend liberal values and America after Second World War “to sustain economically and politically the foundations of liberal society beyond its borders”. Hence national security lies in ensuring that other nations also follow liberal principles and that having a like minded philosophy, prevents wars between nations that adhere to liberal principles.
The first effect of liberalism on foreign relations was that it brought peace among nations in the 19th century. For over 200 years there has been a near absence of war between any two liberal states. However, the same has not been the case with non-liberal states. Feudal states in Europe engaged in almost continuous conflict in the 18th and 19th century. Fascist states fought amongst themselves in the 1930s.
Liberalism provided a common platform for enhancing collective security of like minded nations and also acted a tool for forming alliances in times of aggression by non-liberal nations. The Second World War offers a striking example of how a predominantly liberal grouping of nations aligned together to defeat the non-liberal fascist regimes. The Second World War also offers example of how liberalism could combine realism and pragmatism by aligning with a non-liberal state- Russia to defeat fascist nations and later turn on its old ally Russia to counter threats to liberal values.