Scorched earth

A scorched earth policy is a military strategy or operational method (possibly more often referred to as a tactic, but this is not entirely correct, as there is a difference between the terms) which involves destroying anything that might be useful to the enemy while advancing through or withdrawing from an area. Although initially referring to the practice of burning crops to deny the enemy food sources, in its modern usage the term is not limited to food stocks, and can include the destruction of shelter, transportation, communications and industrial resources. The practice may be carried out by an army in enemy territory, or its own home territory. It is often confused with the term "slash and burn", which is not a military method but rather an agricultural technique. It may overlap with, but is not the same as, punitive destruction of an enemy's resources, which is done for purely strategic/political rather than strategic/operational reasons.
Source: http://en.wikipedia.org/wiki/Scorched_earth