The dawning of the Atomic Age brought new concerns of international security to the world — who should regulate this incredibly destructive potential? In the words of atomic pioneer Albert Einstein, "The release of atomic energy has not created a new problem. It has merely made more urgent the necessity of solving an existing one" — the struggle for peace.

The Cold War which followed close on the heels of the end of World War II was centered around the alarming potential for nuclear war. The public became conversant with frightening concepts like "MAD", or mutual assured destruction, which meant that the U.S. and U.S.S.R. were stalemated by the ability to launch a counterattack after a first nuclear strike. "Duck and Cover" was the instruction given to civilians, and public school children as a measure against fallout from an atomic blast. Atomic defense became a key political issue. Even a former general like Eisenhower couldn't escape being painted as weak on defense. His critics made much of a "missile gap," contending that the nation had fallen behind the Soviet Union in the production of nuclear missiles.

• CNN's THE COLD WAR
• The Atomic Archive

International attempts to regulate nuclear technology and weapons began almost immediately after the end of World War II. Two of the Allied leaders pointed out the challenges in 1946:

It would nevertheless be wrong and imprudent to entrust the secret knowledge or experience of the atomic bomb, which the United States, Great Britain, and Canada now share, to the world organization, while it is still in its infancy. --Winston Churchill, "Iron Curtain" Speech, 1946

I believe it possible that effective means can be developed through the United Nations Organization to prohibit, outlaw, and prevent the use of atomic energy for destructive purposes. --Harry S. Truman. State of the Union Address, 1946

Following the Cuban Missile Crisis of 1962, the U.S. and the U.S.S.R. took a tentative step in early 1963 to establish a direct communications link — the "Hot Line" between heads of state. It wasn't until late 1963 that the first substantive nuclear treaty was signed. The Nuclear Test Ban Treaty, the first trilateral agreement negotiated by the two superpowers and the UK, prohibited tests of nuclear devices in the atmosphere, in outer space, and underwater. It allowed nuclear testing to continue underground, so long as radioactive debris is not allowed "outside the territorial limits" of the testing state. The treaty was later signed by 116 countries. In 1992, China exploded a bomb beyond the treaty limits.

The second major international agreement was 1968's Nuclear Non-Proliferation Treaty, designed to limit the spread of nuclear technology. The United States, the Soviet Union and the United Kingdom promised not to provide technical information to countries seeking to join the nuclear club, and agreed to "pursue negotiations in good faith" toward ending the arms race. Non-weapon states agreed not to get nuclear arms and agreed to allow U.N. International Atomic Energy Agency to oversee their nuclear facilities. The treaty has since been signed by 187 countries and was extended indefinitely in May 1995. India, Pakistan, Israel and Cuba are the only UN members that haven't signed on. India and Pakistan tested nuclear devices in 1998, and Israel is believed to have nuclear capability.

• Text of the Test Ban Treaty
• More on underground testing

Nuclear weapons diplomacy took a different turn in the 1970s, toward the limitation or elimination of certain classes of weapons in order to undercut the arm or missile race. In 1972 the U.S. and the U.S.S.R signed the Anti-Ballistic Missile Treaty which limited anti-missile defenses to two sites in each nation.

That same year the two signed the Strategic Arms Limitation Treaty (SALT I) further limited testing and use of nuclear weapons systems.

In 1987 the first nuclear arms control agreement to actually reduce nuclear arms, rather than establish ceilings, was ratified. The Elimination of Intermediate-Range and Shorter-Range Missiles (INF) required the elimination of all missiles with ranges between 625 and 3,500 miles by June 1, 1991, and all missiles with ranges between 300 and 625 miles within 18 months. In all, over 2,500 missiles were to be eliminated. Critics contend that the 1983 Strategic Defense Initiative or "Star Wars" program would have undermined these missile treaties.

• Text of the INF Treaty
• FRONTLINE: The Missile Wars

START treaty negotiations aimed to significantly reduce the U.S. and U.S.S.R's nuclear arsenals by 30 percent. START I was followed by 1993's START II, which called for a two-thirds reduction in long-range nuclear weapons. But history soon caught up with the treaty — the break-up of the Soviet Union, left nuclear weapons in a group of newly independent states.

The current treaty at issue is the Comprehensive Test Ban Treaty, first opened for signatures in 1996. This multilateral agreement bans all nuclear tests above and below the Earth's surface. The treaty also established a worldwide monitoring system to check air, water and soil for signals that someone set off a nuclear explosion. While President Clinton signed the treaty, in 1999, the U.S. Senate refused to ratify it. The treaty does not fully go into effect until 44 nations that are members of the UN Conference on Disarmament have signed and ratified the agreement. The three nations among the 44 nuclear states that have neither signed nor ratified the treaty are India, Pakistan and North Korea, each of which continues to test nuclear weapons.

• START I Treaty text
• The Comprehensive Nuclear Test Ban Treaty, United Nations
• ONLINE NEWSHOUR: The Nuclear Test Ban Treaty
• ONLINE NEWSHOUR Forum: Post Cold War Defense