It is a war crime for an aggressor to settle its citizens in a conquered area.
Is it the most serious of war crimes? No, initiating a war is the most serious of war crimes.
Why is it a war crime, when an exactly similar settlement of foreign citizens may be legal in times of peace? Well, a peacetime settlement by foreigners would occur through the invitation of the host country, or through the normal process of paying for land from people who are willing to sell. Settlement during or after a war indicates a plan to retain territory conquered in a criminal manner. It is like the difference between an honest trade and a theft.
Why bring up this topic now? Because today the United Nations Office of the High Commissioner for Human Rights released a preliminary report noting that the most recent Israeli settlement in eastern Palestine violates this war crimes law. The implications are large. [See the Press release, Israeli settlements symbolize the acute lack of justice experience by Palestinian People, which links to the full report.]
Is there a statute of limitations on war crimes? I don't think so, though there probably should be. I know the Israeli and other governments continue to hunt down and prosecute alleged war criminals from the Nazi era, over sixty years ago.
If there is no statute of limitations on war crimes, or if the statute of limitations is 60 years, then the entire state of Israel is in trouble. Most Jews in Palestine had converted (perhaps not voluntarily) to Islam by about 700 A.D. Jewish communities that remained were small until the Zionist movement of the late 19th century. The early Zionists were legal immigrants, and as a result several small areas of Palestine had Jewish majorities by World War II.
Most of the post-war Jewish immigration to Palestine can be characterized as illegal. The war that established the State of Israel in 1948 coincided with the ejection of non-Jewish Palestinians, followed by Jewish settlements on their land. Thus it is not just the remnants of Palestine, the West Bank and Gaza, that are at stake. The creation of the State of Israel can be characterized as a war crime.
It is often said that the United Nations (then newly formed, and basically a war organization for fighting Germany and Japan) created the State of Israel. It appears that all the U.N. did was endorse a Jewish semi-autonomous partition zone within Palestine. But supposing the U.N. did in fact back the creation of Israel by settling Jews on lands taken from Palestinians. Then the U.N. itself should be said to have committed a war crime.
The implications are staggering the further we go back in history. What if, after a war of aggression takes place, there is a peace treaty? Does that make it legal to settle on land occupied in a war of aggression? Peace treaties tend to be imposed by aggressors. They are not really voluntary agreements.
What about the settlement of Europeans in colonial nations? What about the United States, which would not exist except for a constant clamor of wars, occupations, and settlements?
If the purpose of war crimes laws is to stop wars and war crimes, then they must be enforced. American settlements occurred, in the main, before the war crime laws were written. Israel, however, creates a different case. It came into existence after the war crimes laws were on the books.
But the real question is, will anyone enforce the war crimes laws? Conquered nations like Japan and Germany have had their leaders prosecuted for war crimes. But no victorious nation has ever been prosecuted for war crimes.
Like Hitler marching into Russia, it looks like the Israeli occupation of eastern Palestine has gone too far, endangering the entire Israeli project. A sane leadership of Israel would cut their losses to hold onto their gains. A sane leadership would trade forgiveness for their earlier crimes against humanity and war crimes in order to hold onto the lands gained by those crimes. A sane leadership would offer to remove all Jewish settlers to Israel proper, in return for an immediate and permanent peace.