A scorched-earth policy is a military strategy of destroying everything that allows an enemy to be able to fight a war, including water, food, humans, animals, plants and any kind of tools and infrastructure. Its use is possible by a retreating army to leave nothing of value to the attacking force or by an advancing army to fight against unconventional warfare.
Scorched earth against non-combatant has been banned under the 1977 Geneva Conventions.
It is prohibited to attack, destroy, remove, or render useless objects indispensable to the survival of the civilian population, such as foodstuffs, agricultural areas for the production of foodstuffs, crops, livestock, drinking water installations and supplies, and irrigation works, for the specific purpose of denying them for their sustenance value to the civilian population or to the adverse Party, whatever the motive, whether in order to starve out civilians, to cause them to move away, or for any other motive.
The term was found in English in a 1937 report on the Second Sino-Japanese War. Retreating Chinese burned crops and destroyed infrastructure like cities to sabotage the logistics of the advancing Japanese forces.
Clausewitz wrote in Principles of War:
In defensive just as in offensive warfare, it is necessary to pursue a great aim: the destruction of the enemy army, either by battle or by rendering its subsistence extremely difficult. Thus we shall disorganize it and force it into a retreat, during which it will necessarily suffer great losses. Wellington's campaign in 1810 and 1811 is a good example.
Clausewitz wrote in On War:
All that the country yields will be taken for the benefit of the retreating army first, and will be mostly consumed. Nothing remains but wasted villages and towns, fields from which the crops have been gathered, or which are trampled down, empty wells, and muddy brooks.The pursuing army, therefore, from the very first day, has frequently to contend with the most pressing wants.