In a Science Fiction Story About Hostile Aliens Invading Earth

In a science fiction story about hostile aliens invading Earth, the major conflicting political powers join together to combat the extraterrestrial threat. Based on Muzafer Sherif's research, it would be safe to conclude that this act of cooperative behavior would lead to:

A) cognitive dissonance on a national level rather than on a social group level.
B) alienation, antagonism, and increased levels of conflict once the threat is over.
C) increased conflict over which group should get the most credit for defeating the aliens.
D) reduced conflict and increased harmony between the major powers.