The Israeli occupation of Palestinian territories (the West Bank including the Old City of Jerusalem and the Gaza Strip) is now in its fifth decade. The occupation started after Israel’s decisive victory in the Third Arab-Israeli War or what is sometimes called the Six-Day War (June, 1967). Why Israel is still there is an excellent question but one that the international community cannot agree on.
Many, including the United Nations, will argue Israel is violating international law by not only continuing to occupy but also by expanding their settlements in the occupied areas. I think Israel believes they have a right to be there because they won the war in 1967 and the land now belongs to them.