Bombing diplomacy refers to bombing another side into submission. It is used interchangeably with coercive diplomacy. Like coercive diplomacy, bombing diplomacy is a contradiction as a term, as diplomacy does not include use of force.
One example of bombing diplomacy is the bombing of North Vietnam by the USA during the Vietnam War. The USA used bombing as a tactic to try to bring North Vietnam to the negotiating table. However, the bombing raids often caused more civilian deaths than military ones, leading to criticism from many quarters. The bombings ultimately failed to bring about any tangible results and were seen as a largely ineffective form of diplomacy.