Which of the following actions of territorial aggressions by nazi germany ultimately resulted in a declaration of war by great britain and france?
a. the invasion of poland
b. the militarization of the rhineland
c. the movement of troops into czechoslovakia
d. the reattachment of the saar region to germany

The reason why Great Britain and France declared war on Germany at the beginning of the second World war was because A - The invasion of Poland.

When Germany invaded Poland this was the beginning of what would later be called the second World war. A tense atmosphere was brewing up in Europe for a few years since then already because when Hitler's party took charge of Germany, it increasingly militarized the country and was preparing it for war.