Nato officials say half a million people have been displaced so far in Kosovo, as a result of what they call a protracted campaign of ethnic cleansing against the local Albanians.

The wars in former Yugoslavia mark the revival of a traditional way of conducting warfare, which many thought had come to an end, in Europe at least.

Nato justifies its attacks on Yugoslavia by saying it is trying to prevent the massacre and displacement of the Kosovo Albanians.

Opponents of the bombing say Nato has no right to intrude in the internal affairs of a sovereign state of which Kosovo is a recognised part.

Legal arguments apart, the fact that refugees are crossing into neighbouring states, means that in practical terms this is no longer just an internal Yugoslav issue.

Byzantine legacy

Military action directed at civilians has been a familiar aspect of warfare.

Opponents say the crisis is an internal affairs of a sovereign state

In the Balkans, the medieval Byzantine Empire conducted military campaigns aimed at rounding up local populations and resettling them in other parts of the empire - a practice continued by the Ottoman Turks.

The Americans, too, have a dubious record of targeting civilian populations within their own territory - whether in repeated expulsions of native peoples from their homelands or the "scorched-earth" campaigns conducted by Union armies in Southern states like Georgia, Virginia and South Carolina during the Civil War.

Russian expertise

The Russians have been noted exponents of "ethnic cleansing".

The brutal 19th century conquest of the Caucasus was accompanied by massacres and the deliberate destruction of towns and villages and the mass exodus to neighbouring countries like Turkey and Iran of Chechens, Circassians and other local peoples.

The deliberate targetting of civilians as a method of warfare reached an all-time climax during WWII.

The German airforce deliberately strafed refugee columns - in Poland, the Netherlands, France and elsewhere - as a way of spreading panic and disrupting defence.

The wave of killing and raping that accompanied the advance of the Soviet army into Germany in 1945 is thought to have been deliberately encouraged to prompt the flight of German civilians from territories earmarked for annexation.

Hague ban

The 1907 Hague Convention on Land Warfare forbids looting and mistreatment of civilians in occupied territories.

Needless to say, its provisions have been widely flouted.

That treaty applied to war between states. But after the border changes that followed World War I, several Central and East European countries were forced to sign international agreements pledging respect of minority rights.

Britain and France, of course, saw no need to apply the same rules to themselves - teaching in Welsh or Breton being expressly forbidden in state schools at the time.

Right to intervene

Though never explicitly codified, the right of intervention in countries' internal affairs has been implicitly recognised in recent decades.

The principle can be found in UN Conventions, in the human-rights provisions of the 1975 Helsinki Agreement or in the de-facto acceptance of a Soviet sphere of influence in Central and Eastern Europe during the Cold War.

The Nato attacks on Yugoslavia, however, take the debate on to a different plane.