In post-WWII Western European politics, liberals such as David Mitrany studied the nature of international collaboration and how it could be achieved through apolitical processes in his integration theory named “functionalism”. According to Mitrany, nonpolitical experts could better deal with their areas of technical expertise and initiate collaboration which in time would expand into other areas as well. The ever closer union of Western Europe increased the attention towards liberal integration theories and the question evolved this time around whether political integration could be achieved or not.

Ernst Haas was the one putting forward the assumptions of "neofunctionalism".

The most well-known liberal internationalist Wilson in the aftermath of the WWI argued for a system of collective security to maintain peace, based on rule of law, instead of the old balance of power mechanism.

Robert Keohane listed three strands of classical liberal theory as (1) commercial liberalism about the pacific effects of trade, (2) democratic liberalism about pacific effects of republican governments, (3) regulatory liberalism about rules and institutions for relations between countries. Joseph Nye has added a fourth one (4) sociological liberalism about the effects of transnational ties on national attitudes and interests.

The term interdependence (mutual dependence) entered the liberal terminology and was followed by the term transnationalism, which further supported liberalism’s pluralistic nature as regards international actors. The rise of the multinational corporations (MNCs) in world politics and their business transactions across the national boundaries of sovereign nation states increased the interest towards international political economy. The transgovernmental coalitions of the MNCs began to have steering role in economics and were closely related with politics as studied by Nye and Keohane.