This term is
generally used to refer to a war in which two
nations with
nuclear arsenals fire
nuclear weapons at each other. It is not commonly used to refer to a group other than a
government, such as a
terrorist organization using nuclear weapons to attack a target, or to refer to a nation with
nuclear weapons firing them at a nation without nuclear weapons. It usually refers to delivery by
airplane or
missle rather means involving less
technology, which might instead be classed as
terrorism.
Most analysts currently believe India and Pakistan are the two nations most likely to be involved in a nuclear war. It even seems likely that none of the major world powers would use nuclear weapons in that event - at least not immediately.
The most likely catalyst for such a war is the tension over Kashmir, a region which has been claimed by both countries since they became seperate nations.
A nuclear war would have long term effects on both participants and at least some uninvolved bystanders, perhaps after the original causes of the war were forgotten, as large areas become contaminated by radioactivity, and radiation as carried to different places by air and water circulation.