Well... I believe that the answer to your question is A. because if the Emperor would have to ask the pope if they could go to war and the pope was the one who crowned the Emperors.
Manifest destiny affected native americans' lives because the white colonized men who believed they should move west and spread their religion forced indian americans to leave their land and claim it as theirs.
I understand the war is the World War I. The assassination (of Austrian Crown Prince Franz Ferdinand) led to the Ultimatum (from Austria to the Kindom of Serbia) and the rejection of this ultimatum by Serbia led to Austria-Hungary declaring war (into which later other countries joined).
The answer would be the invasion of CAMBODIA