The third phase (2019-23) would see the global zero accord legally agreed on and signed by all nuclear-capable states.

ECONOMIST: Banning the bomb will be hard, but not impossible

The first phase, intended to run from 2010-13, required America and Russia to negotiate a bilateral accord to reduce their total warheads to 1, 000 each from their current inventories of, respectively, 8, 500 and 11, 000 (the two countries still account for 95% of the world's 20, 500 nuclear warheads).

ECONOMIST: Banning the bomb will be hard, but not impossible