Air attacks on a city that treat it as a single military objective instead of clearly distinguishing military objectives and attacking them individually are an example of area bombardment, often called carpet bombing. Many of the World War II attacks on cities targeted an area rather than individual military objectives. Legal arguments and military rationales were given for the strategic bombing campaign, among them to destroy the enemy’s industry, to weaken the morale of the population, or simply to punish the adversary for its previous violations. The destruction of Rotterdam, Dresden, and Hiroshima are prominent examples. The Nuremberg Tribunal did not discuss area bombardment in any detail, and the practice, which flies in the face of all the civilian protections in the Fourth Geneva Convention of 1949, continued into the Cold War. The U.S. aerial campaigns against North Vietnam—in particular the so-called Christmas bombing of 1972 against Hanoi and Haiphong—are believed to have been illegal area bombardments.

An explicit ban on area bombardment was first codified in the 1977 Additional Protocol I, which applies to bombardments of cities, towns, villages, or other areas containing a concentration of civilians. An attack by bombardment by any methods or means that treats as a single military objective a number of clearly separated and distinct military objectives is considered to be an indiscriminate attack and is prohibited. Launching such an attack in the knowledge that it will cause excessive loss of life, injury to civilians, or damage to civilian objects is considered a grave breach. Bombarding areas containing solely military targets is permitted. Important powers such as the United States, which are not party to Protocol I, accept this principle as binding customary international law.

Though the Protocol’s wording makes it clear that attacks targeting cities as such are prohibited, declarations by States while negotiating the text suggest severe problems in applying it. States have made clear that “clearly separated” implies a significant distance between separate military objectives, but what is “significant” is highly subjective.

One obvious problem is the inaccuracy of aerial bombardment. This has been altered by newer precision-guided weapons; but these are available
only to a few combatants, and then, only in limited quantities. So long as the party to the conflict attempting to distinguish between targets employs weapons that can be used discriminately, it will be able to claim it has avoided crossing the line into violations of humanitarian law.

From recent conflicts it can be concluded that belligerents are aware of the restraints on area bombardment even if they are not bound by the rules of Protocol I. The major allied forces in the Gulf War claimed to have implemented the standards of Protocol I in attacking Iraqi military targets although not bound to do so.

The U.S. military command has acknowledged that the bombing of the Iraqi Basra area by American B-52 bombers in 1991 was an area bombardment. As the attacks had been directed solely against the combatants of the so-called Iraqi Republican Guard, the United States believed the attacks to have been lawful.