Final answer:
Hitler's statement refers to the concept of uniting a nation at critical junctures, aligning with his expansionist policies aiming for the consolidation of German-speaking people and the acquisition of 'Lebensraum', which were key in the lead-up to World War II.
Step-by-step explanation:
When Hitler writes “an ancient instinct admonishes all peoples to set aside internal controversies when the fatherland stands at the decisive hour for political action,” he means that there is a deep-seated tendency among nations to unite and put aside internal disputes when their country is facing a crucial moment that requires political and possibly military action.
This message was consistent with Hitler's broader goals and ideology that he detailed in Mein Kampf, where he emphasized the importance of uniting all German-speaking peoples and the conquest of living space (“Lebensraum”) for the pure German “Aryan race.”
The unity he speaks of was intended to rally the German population around his aggressive expansionist policies, which eventually led to World War II after he had successfully annexed Austria and then invaded Poland.