21.   State Department officials said it was the worry about a possible nuclear exchange between India and Pakistan that helped tipped the balance toward getting Americans out.

22.   The greater fear, however, is of a conflict that could spiral into a nuclear exchange.

23.   The greater fear, however, is of a conflict that could spiral into a nuclear exchange between the countries, which have a million troops on their border.

24.   The United States still presumes a series of nuclear exchanges based on exceptionally deep rivalries and differences.

25.   The war simulations in which he has participated almost always end with a nuclear exchange.

26.   These escalations could very easily have spiraled into a nuclear exchange.

27.   This time out the nuclear exchange is between the United States and China, triggered by a crisis over Taiwan.

28.   What might begin as a limited military action could escalate into a nuclear exchange.

29.   Another war between India and Pakistan could include a nuclear exchange, former U.S. defense secretary William Perry said Saturday at an arms control symposium.

30.   But many analysts believe that a future confrontation between the South Asian rivals could quickly escalate into a nuclear exchange.