What is the True Meaning of the Term 'Leader of the Free World'?

Meaning of 'leader of the free world'
The term 'Leader of the Free World' originated in the Cold War era. It was a colloquialism referring to the United States and/or the U.S. President. Buzzle helps you find out more about its meaning, and how it changed with time.
American Exceptionalism
It is a theory which states that, the United States is unique due to its democratic ideals and values as a free nation.
In a glance at this particular phrase, we may think of it as some sociopolitical concept in international politics or international philanthropy. Nonetheless, it is not something totally opposite or anything completely contrasting to human welfare either.

The term has been viewed in different light by every individual in the capacity of a historian, political commentator, journalist, or leader of some nation. To understand its meaning, we should begin with how it originated, in what context, and then see if and how it is relevant to the world today.
Origin of the Term 'Free World'
The world was more or less divided into two poles during World War II - the Allied and the Axis powers. The countries of Japan, Germany, and Italy, forming the Axis group, were identified for their oppressive and expansionist policies. Italy was the source of fascist ideology, or the form of radical nationalism that was totally against liberalism. The Allied powers opposed such authoritarian ideology and dictatorship, as seen to be practiced by the Axis powers. So, the Allies were named as an alliance of the 'free nations'.

In the aftermath of World War II and during the Cold War, the concept of 'Free World' was born. This referred to that part of the world which was 'free'. Primarily, this meant all the capitalist nations, excluding the communist countries. Also, the idea of freedom of speech, press/expression, thought, and association determined these countries as 'free'.

Interestingly, going by the meaning of the term, during the second World War, the Soviet Union forms part of the free world. However, if considered during the post-war period, it does not fall under the category of free world.
Meaning of 'Leader of the Free World'
John Fousek, in his book To Lead the Free World, maintains that the idea of free-world leadership had become the controlling metaphor in the U.S. foreign policy discourse in the post-war period. He therefore goes on to say,

"The Free World, in this view, was a metaphor, depending on one's viewpoint, for the capitalist world system or the anticommunist bloc."
The beginning of the Cold War is generally traced back to the Truman Doctrine (presented by U.S. President Harry S. Truman in March 1947). He defined the Doctrine in the joint session of Congress as, "The policy of the United States to support free people who are resisting attempted subjugation by armed minorities or by outside pressures." The U.S. had then agreed to support Greece and Turkey economically and militarily, to avoid Soviet Union's control over them.

Looking at the post-World War II scenario, and emergence of the United States as the strongest nation in the world, we can decipher how the phrase 'Leader of the Free World' was grounded. The term was identified with the President of the United States and/or the United States itself, as the leader of the most powerful democracy of the world.

America has been perceived to champion the cause of freedom. The entire idea of liberty stems from the American history of independence, which has inspired many other nation-states towards attaining the status of a free state. The concept of 'individual freedom' led to the human rights movement, and its spread the world over. These impressions that the U.S. has made upon the world, or strives to make even today, as the representative of the ideal of liberty, gives it the identity of a leader.
During the Cold War, there were several countries which were neither allied to NATO (North American Treaty Organization) nor to the Communist Bloc. These non-aligned 'Third World' countries, as referred to then, perceived the leadership of the United States as illegitimate and showing unnecessary grandeur. It was also said to be a medium of propaganda, while the United States was engaged in an indirect, but continuous confrontation with the Soviet Union until the dissolution of the USSR. The American intervention in Vietnam was executed as a responsibility that the U.S. had of protecting free people from aggression, and containing communism. However, the Vietnam war, in fact, questioned the validity of the intervention.

The phrase 'Leader of the Free World', with reference to both, the U.S. President and the United States, no longer holds true, irrespective of the fact that the U.S. stands to be a major world power even today. So, we can conclude that it is difficult to ascertain the U.S. or any one country, despite its economic, political, or military strength, to be leading other countries for a specified purpose, like upholding of the principle of liberty, or something as large as world peace.