Scorched earth is a military strategy which involves destroying anything that might be useful to the enemy and withdrawing from an area. The name refers to the practice of burning crops to deny the enemy food sources. The practice may be carried out by an army in enemy territory, or by an army in its own home territory, as in World War II Soviet/Nazi example.
Wars which have involved a scorched earth policy
Scorched Earth is also the name of a popular computer game.
See also Total war.