The Basic Law for the Federal Republic of Germany is occupation law.
It is a self-commitment of the FRG to the Allies.
It is neither a treaty, like the State Treaty of Austria, nor a constitution.
How could it be written in a constitution that it loses its validity on the day a constitution is proclaimed?
Article 146 GG Duration of the Basic Law

This Basic Law, which, since the achievement of the unity and freedom of Germany, applies to the entire German people, shall cease to apply on the day on which a constitution freely adopted by the German people takes effect.

Primacy of international law

The general rules of international law shall be an integral part of federal law. They shall take precedence over the laws and directly create rights and duties for the inhabitants of the federal territory.

The general rules of international law: these include, for example, the Treaty of Versailles, the Convention Respecting the Laws and Customs of War on Land (Hague IV.).
 
The FRG is therefore obliged to observe the Versailles Treaty, just like the Hague IV.
 
These treaties take precedence over all German laws: i.e. all laws that contradict these treaties are illegal.
 
These treaties create rights and duties: i.e. the FRG is obliged to observe them.
 
These treaties create duties directly for the inhabitants of the Federal Republic: i.e.
1. all inhabitants are obliged to abide by these treaties - all inhabitants means that even those who are not Germans but only have their residence in the FRG are obliged to abide by these treaties.
2. direct means that no inhabitant can retire to his couch and claim that politicians are responsible if this international law is not respected
It does not say: directly for the Members of the Bundestag.
It says: directly for the inhabitants.
 
Example: The deprivation of the Nazig nationality of Mr Beowulf von Prince is, among other things, a breach of the Treaty of Versailles and of UN Human Rights, EU Human Rights:
The deprivation of nationality is forbidden!
The nationality Free City of Danzig is part of the Treaty of Versailles.
The perpetrators of the deprivation of nationality of the Free City of Danzig were convicted and executed at the Nuremberg War Crimes Trials.
This means that every inhabitant of the territory of the Federal Republic of Germany is obliged - directly obliged - under the Basic Law to ensure that the persecutions for Danzig cnationality are brought to an end.

Example: unlawful, dependent and biased judges:
This is also forbidden under the UN Human Rights, International Covenant on Civil Rights and EU Convention on Human Rights.
This means that every inhabitant of the Federal Republic of Germany is obliged - directly obliged - under the Basic Law to ensure that the independence, legality and impartiality of judges in the FRG is established.

This Article obliges to resist if international law is no longer respected.
Many refer to Article 20 of the Basic Law. There the right is there.
But here is the duty! Nobody may therefore be condemned in the FRG for the performance of his duty.
But this happens! So it is no longer the FRG that acts according to the Basic Law, but the German Reich with the law of 1945.

Article 25 of the Basic Law refers to general international law. This includes, as already quoted above, the Hague IV.
Article 25 of the Basic Law refers to Article 25 of this Hague IV. Convention. There it says that the attack on unfortified cities, i.e. civilian population is forbidden. But that is exactly what the Nazis did. They declared the Free City of Danzig a fortress. A fortress can be completely destroyed in a war.  In doing so, they left the Free City of Danzig to total destruction. This means that the civilian population and refugees were misused as protective shields. The protection which the Hague IV. Convention granted to the civilian population in Article 25 was abolished.
This was charge number one of the Nuremberg War Crimes Trials.
The Nazis also had no mercy for the civilian population of other cities, such as Breslau, Königsberg etc., which were also declared fortresses. In Berlin, the Allies were forced to wage a house-to-house combat forbidden by the Hague IV. Convention, at a time when the war had long since been lost. The Allies did not have to get involved.
Ask yourself: If one party to a war no longer adheres to a treaty, is the other party still obliged to honour it? The logical consequence is that if the own nationals have already abandoned the population to total annihilation, the opponent can claim the same right. He does not have to conquer house after house in a bloody house-to-house combat...
That this will never happen again, it was written into the German Basic Law that the Germans are directly obliged to resist and can no longer invoke any oaths.