Military or belligerent occupation is hostile control by a ruling power over a sovereign territory that is not part of the ruling power's own sovereign territory. The controlled territory is called occupied territory, and the ruling power is called the occupant. During a military occupation, the occupier has certain responsibilities to uphold public order.
Hundreds of years ago, the old notion of "to the victor belong the spoils" was replaced with the new notion that sovereignty was not to be taken from a state by force. Military occupation, which is a loss of a sovereign's control of a territory, but not a loss of sovereignty, was thus considered temporary. Ideally, a peace treaty would soon return control to the ousted sovereign.
Once control is established, occupation begins. This is captured by a partial award of the Eritrea-Ethiopia Claims Commission (2004) which stated that 'where combat is not occurring in an area controlled even for just a few days by the armed forces of a hostile Power, the Commission believes that the legal rules applicable to occupied territory should apply.
The law of belligerent occupation evolved slowly with an increasing and consistent movement toward justice and humanity. Prior to the last century, in the absence of any international code of conduct, the belligerent occupant dominated the occupied territory and its citizens. The principle or idea which guided the combatants—in this lawless setting—was 'to the victor belong the spoils.' At the same time, no real distinction was made among military occupation, conquest, and subjugation.