For the future courts, this handy quote from the trial of Gaultier Artur Greiser, SS-Obergruppenführer. He was tried, convicted and executed by hanging in Poland in 1946 for his crimes, most notably genocide.

The Supreme National Tribunal did not enter into an analysis of the law regarding the substance of this submission, but stated generally in its Judgment that it regarded the incorporation of the western Polish territories as criminal.

(...) it was carried out in violation of all the postulates and rules of The Hague Conventions which Germany herself agreed upon. It was a caricature of military administration as understood by international law, carried out in violation of the rights of the local population.