Earlier quoted context omitted.
"suddenly" Poland refused to negotiate on a land bridge to East Prussia and a compromise on Danzig governance because daddy Britain said they didn't have to. Germany's brutality was not justified, but it's not as if it happened suddenly.
It is sudden as it was an overreaction.
Man A is pushing man B repeatedly and yelling at him as a bar dispute escalates. Man B pulls out a gun and shoots man A.
Overreaction? Yes. Sudden? Not necessarily.