Liberalism is one of the dominant theories of International Relations which holds that human nature is basically good. It was also illustrated by John Lock and Montesquieu, who argued that human nature is perfect. Problems arise as humanity enters in civil society. Simply, liberals believe that war is the product of state not in an inherent attribute to individual.
In 19th century, liberalism added democracy and free trade itself. However, liberal internationalists openly said that individual only achieves their needs in a democratic state, unrestricted by any government. Likewise, political freedom can solely be achieved in capitalist states.
The argument of liberal internationalists that free trade automatically brings peace or capitalism, is inherently peaceful, had been criticized by liberal idealists. One of the propositions of this idea is of Woodrow Wilson. According to liberal idealists, war is preventable through collective action of states, such as League of Nations.
As per them, capitalism has led to bundle of production of goods which caused under consumption. Wars occur in international system for markets, as the experience of both the great Wars tell.
Liberal idealism strongly came with the idea of collective security, democracy, right of self determination and open agreement. In fact, half of the League covenant’s twenty six (26) provisions focus on preventing wars, but why World War 2 happened? This question led liberal institutionalists to take the stage. They developed liberalism with more complicated, according to which world war 2 happened because there had been empty place for some great powers in international system.
In 1945, United Nations Organization was established with five veto powers and some permanent members of security council. But, with passage of time, liberalism came under intense criticism and liberalism as a theoritical perspective fell out of favour.
In the end of Cold War 1919, liberalism as a general theoritical perspective achieved new credibility with the ideas that, democratic states are as war like as autocratic, but they never attack each other. Because, contemporary liberalism believe democratic precess prevent aggression and international institutions do not allow them.
However, one of the pessimistic arguments of contemporary liberalism is, to replace dictator with democratic government which reduces the chance of war, but the US invasion of Iraq in 2003 in intention to regime change was a human rights violation.
Francis Fukuyama, to whom grievance between Israel and Palestine, Armenians and Azeris will continue, because the percentage of conflicts has been declined. The history is end from liberalism and “Possibility exists for the universalization of western liberal democracy as the final form of human governance,” which he presented in his famous article ‘The end of history’ after cold war.