Post World War II

World War II brought American isolationism to an end.
The crucially important Lend-Lease Act (11 March 1941) that, even prior to Pearl Harbor, introduced the United States into the front stage of world diplomacy and at the same time gave the latter an entirely new form.
Traditional diplomacy had been conducted between great and small powers, and Wilsonian diplomacy had established the principle of equality, diplomacy after lend-lease assumed a dual nature.
On the one hand, relations between nations deemed to be equals continued to be conducted by ambassadors.
On the other hand, there emerged a new form of relationship between two countries, whereby one became the aid donor and the other the aid recipient.
Thereafter, actively involved in the life of the international organization, the United States found that it had adopted Wilsonian “internationalism,” which constituted a break with tradition.
The main preoccupation of American treaties following World War II was security cooperation in a postwar climate characterized by ideological conflict with the Soviet Union, bipolarization of the world between these two powers, destruction of the colonial empires and the emergence of nearly ninety new nations, economic inequality, and reliance on atomic weapons as a deterrent.
Almost all have been of a new type. They have included aid accords, participation in the United Nations, peace treaties, treaties of alliance, treaties linked to deterrence, and treaties dealing with a far wider range of issues than had traditionally been the case: human rights, ecology, the environment and resources, global warming, the outlawing of chemical and other weapons of mass destruction, access to and the future use of outer space, copyright and the protection of intellectual property, and biotechnology and human cloning.
The Treaty of Paris (October 1954), ended the occupation of Germany, replacing it with the presence of “security forces.” These negotiations (between council ministers of five powers) were brought to a halt by U.S. adoption of containment policy (the Truman Doctrine of 12 March 1947 and the Marshall Plan of 5 June 1947), the
creation of the Kominform by the Soviet Union, and the increasing tensions of the Cold War in 1948 (the Berlin Blockade).
The Atlantic Pact of 4 April 1949, which created NATO, was a reaction to the Cold War.
The Warsaw Pact (formally, the Treaty of Friendship, Co-operation, and Mutual Assistance, sometimes, informally War Pac, akin in format to NATO) was a collective defense treaty among eight communist states of Central and Eastern Europe in existence during the Cold War.
(14 May 1955), Motto: Union of Peace and Socialism