Nov. 9 -- East Germany opens the Berlin Wall, signaling the collapse of communism in Eastern Europe.
July 31 -- US and the Soviet Union sign the Strategic Arms Reduction Treaty, or START I. It cuts the number of nuclear weapons in each country's arsenal. Is effective as of December 1994.
Dec. 8 -- The Slavic republics of Russia, Ukraine, and Byelorussia declare the Soviet Union dead and establish a new 'commonwealth.' Later in the month, Soviet President Mikhail Gorbachev resigns, and the country's legislature votes the Soviet Union out of existence.
October -- Congress establishes the Cooperative Threat Reduction program - the largest US effort to secure or destroy weapons of mass destruction from the former Soviet Union.
Nov. 27 -- The European Community, Japan, Russia, and the US establish the International Science and Technology Center, in Moscow, to employ weapons researchers from the former USSR in civilian science projects.
Jan. 3 -- US and Russia sign START II, a treaty that calls for further reductions in nuclear weapons. It is not yet in force.
Feb. 18 -- Under the Highly Enriched Uranium Purchase Agreement ('Megatons to Megawatts' program), the US agrees to buy 500 tons of HEU from Russia over 20 years. The US will dilute it to low-enriched uranium and sell it as fuel for nuclear-power plants.
Jan. 14 -- US, Russia, and the Ukraine sign a trilateral statement that commits the Ukraine to rid itself of nuclear weapons and to transfer specified warheads to Russia over a 10-month period.
Sept. 24 -- The US, Britain, China, France, Russia, and 50 other nations sign the Comprehensive Nuclear Test-Ban Treaty, which prohibits all nuclear explosions. As of August 2001, 79 nations had approved the treaty, but 82, including the US, have signed but not ratified it.
May 11 -- India announces it has conducted a series of successful underground nuclear tests, the country's first in 24 years. The event breaks an international de facto moratorium on nuclear testing. Later in the month, Pakistan announces that it has also exploded nuclear devices.
May 20 -- At a Nuclear Non-Proliferation Treaty review conference, more than 185 signatories approve Thirteen Practical Steps. The measures outline how the treaty's nuclear-disarmament provision can be implemented. For the first time, nuclear-weapons countries commit to eliminating their arsenals.
June 4 -- President Clinton and Russian President Vladimir Putin agree to set up a joint warning center for the exchange of information on missile launches. They also provide for the safe disposal of 68 metric tons of weapons-grade plutonium.
Fall/winter -- For fiscal year 2001, $1.5 billion is earmarked for nonproliferation programs run by the Departments of Defense, Energy, and State. The Bush administration's budget request for nonproliferation programs in fiscal 2002 drops slightly to $1.4 billion.
Jan. 10 -- An expert panel urges the US to spend $30 billion over the next decade to help Russia secure its nuclear materials. That stockpile poses 'the most urgent unmet national-security threat' facing the US, the panel reports.
Sources: Center for Nonproliferation Studies, Monterey Institute of International Studies; Council for a Livable World Education Fund; The Associated Press