The New START Treaty, initially signed by the United States and Russia in 2010, continued a string of nuclear arms control agreements between the two countries stretching back to 1991.
But on 5 February 2026 it expired – leaving no limit on the number of nuclear weapons the US and Russia can stockpile.
The BBC’s Washington correspondent Daniel Bush explains what comes next for nuclear weapons in the 21st century.
Video edited by Alex Foster
