We will study each. They intertwine through the final 20 years of the century.
The Conservatives constructed a different coalition. It consisted of the following four groups:
Through the 20th century transportation began to shrink the world. The invention of the internal combustion engine and the airplane shrank oceans.
The growth of the international corporations with offices and industrial capacity in many nations began to erode economic soverignty. Governments could not legislate controls over companies headquartered elsewhere and often refused to do so lest they lose the corporations they had.
Economic theory of comparative advantage developed to organize world trade. This theory said that different countries possess different advantages economically; those nations should emphasize the domain of their advantage; and world trade should tie these advantaged producutions together in a world economy. Such rhetoric motivated diminished focus on the national market and made markets more world-wide.
International organizations were formed over the course of the century. After the League of Nations failed, the United Nations formed after World War II with multiple agencies under its umbrella. Economic organizations such as the International Monetary Fund, the World Bank, and the World Trade Organization followed. The World Court's involvement increased.
Beginning with the national alliances in the World Wars, even national security was organized through international organizations such as NATO (the North Atlantic Treaty Organization), SEATO (the Southeast Asia Treaty Organization), ANZUS (an alliance of Austrailian, New Zealand, and the United States), the OAS (Organization of American States) and many more.
Finally, the internet served to diminish the distinctions of national boundaries as communication became possible across the boundaries of nation-states.
Displacing nationalism is a difficult rhetorical task. This is a 500 year old rhetoric, intensely saturating humankind. The power of the nation-state to support itself with action based in the rhetoric of nationalism is immense as well. It still explains a lot and provides familiar solutions to problems. The authority structure of world politics remains national. The president is more important that the Secretary General of the United Nations. (Do you know who he is?)
It remains an open question.