The international humanitarian law of occupation contains a prohibition against deporting or transferring parts of the civilian population of the Occupying Power into Occupied Territory, even if they volunteer to be so transferred. Such transfers are often carried out in order to alter the demographic composition of the population of the occupied territory, and constitute a grave breach of Additional Protocol I, as well as being listed as a war crime under the Statute of the International Criminal Court.
As the establishment of settlements also involves population transfers into Occupied Territory, these are prohibited under IHL. Any measure designed to expand or consolidate settlements is also illegal. Appropriation of land to build or expand settlements is similarly prohibited.
MALLISON William T., “A Juridical Analysis of the Israeli Settlements in the Occupied Territories”, in The PalestineYearbook of International Law, Vol. 10, 1998-99, pp. 1-26.
POISSONNIER Ghislain & OSSELAND Pierre, “Les colonies israéliennes de Cisjordanie en droit international”, in RGDIP, T. 114, No. 1, 2010, pp. 63-92.