At the height of the Cold War, the United States and the Soviet Union amassed a combined nuclear stockpile of more than 70,000 nuclear warheads. When Ronald Reagan took office in 1981, he wanted to strike a deal with the Soviets to not only cap the number of warheads held by each superpower—the goal of earlier nuclear negotiations—but also to actively reduce their arsenals.
A decade later, George H.W. Bush and Mikhail Gorbachev signed the Strategic Arms Reduction Treaty, or START I, on July 31, 1991. When the first START treaty was fully implemented, it resulted in the removal of around 80 percent of all nuclear weapons then in existence. Follow-up nuclear pacts, including the New START treaty signed in 2010, further reduced the stockpile, limiting the U.S. and Russia to 1,550 warheads each.
What were the terms of the START I treaty?
The 1991 START I treaty was the first time that the United States and the Soviet Union agreed to reduce their nuclear stockpiles, which had reached peak levels by 1986. The treaty imposed the following limits on each country’s nuclear arsenal:
1,600 intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs) and heavy (long-range) bombers
A total of 6,000 “accountable” warheads on ICBMs, SLBMs and heavy bombers (individual weapons could be armed with multiple warheads)
A maximum payload or throw weight of 3,600 metric tons for each ballistic missile
On the U.S. side, the treaty resulted in the destruction of all 450 Minuteman II launch facilities. START I not only led to a significant reduction in the global nuclear stockpile, but also required unprecedented levels of transparency and cooperation between the United States and the Soviet Union. Each side conducted hundreds of in-person inspections of the other nation’s nuclear sites over the life of the treaty.
Was START II ever enforced?
Not long after START I was signed, the two countries launched negotiations for an even greater reduction of their nuclear arsenals. The START II treaty was signed in 1993 but never enforced due to delays in the ratification process.
One of the goals of START II was to ban all intercontinental ballistic missiles that were armed with multiple independently-targetable reentry vehicles (MIRVs). In addition to eliminating MIRVs, the second treaty aimed to shrink each nation’s total number of nuclear warheads from 6,000 to a maximum of 3,500.
When the two countries failed to ratify START II, presidents George W. Bush and Vladimir Putin met in 2002 to sign the Strategic Offensive Reductions Treaty, or SORT. The SORT agreement imposed steeper reductions in the arsenal, limiting each nation to between 1,700 and 2,200 warheads apiece. However, the SORT agreement didn’t address MIRVs.
When did the New START treaty expire?
The most recent nuclear reduction pact between the United States and Russia was the New START treaty, signed by Barack Obama and Vladimir Putin in 2010 and extended in 2021. It reduced the total number of deployed nuclear warheads to 1,550 per country, a 74 percent reduction from the 6,000 warheads allowed by the original START I treaty. It continued to require close cooperation between the United States and Russia, including notifications each time that a nuclear warhead was moved. More than 25,000 of those notifications were exchanged during the 15 years that New START was in effect.
The New START treaty expired on February 5, 2026, signaling the first time in decades that the world’s two largest nuclear powers were not under any formal nuclear agreement.
