The New START treaty, the last remaining agreement constraining Russian and US nuclear weapons, is due to lapse on February 4.

There are no negotiations to extend the terms of the treaty, either. As US President Donald Trump said dismissively in a recent interview, “if it expires, it expires”.

The importance of the New START treaty is hard to overstate. As other nuclear treaties have been abrogated in recent years, this was the only deal left with notification, inspection, verification and treaty compliance mechanisms between Russia and the US. Between them, they possess 87% of the world’s nuclear weapons.

The demise of the treaty will bring a definitive and alarming end to nuclear restraint between the two powers. It may very well accelerate the global nuclear arms race, too.

The New START or Prague Treaty was signed by then-US President Barack Obama and his Russian counterpart, Dimitri Medvedev, in Prague on April 8, 2010. It entered into force the following year.

It superseded a 2002 treaty that obligated Russia and the United States to reduce their operationally deployed, strategic nuclear warheads to between 1,700 and 2,200 by the end of 2012.

The New START Treaty called for further reductions on long-range nuclear weapons and provided greater specificity about different types of launchers. The new limits were:

These reductions were achieved by February 5, 2018.

The treaty included mechanisms for compliance and verification, which have worked effectively. It provided for twice-yearly exchanges of data and ongoing mutual notification about the movement of strategic nuclear forces, which in practice........

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