There are two main theories in international relations. The realist school sees the world ruled by power and self-interest, or in more Trumpian terms, might and money. The other dominant school is liberal internationalism.
In the aftermath of the Second World War, the United States led by president Harry Truman engaged in a liberal international foreign policy that promoted democracy, state sovereignty and global peace. It was in this era that the United Nations and other global institutions were born, as well as security alliances such as NATO and, importantly for Australia, ANZUS.