Why Did Contact with the Europeans Intensify the Iroquois' Need

Why did contact with the Europeans intensify the Iroquois' need to wage war?

A) The Iroquois needed to increase the power of their Confederacy in order to combat the powerful Europeans.
B) The Iroquois had to prevent neighboring tribes from allying with the Europeans.
C) European expansion constantly pushed the Iroquois from old tribal lands into new unconsecrated territories.
D) As European diseases increased the death rate within the Iroquois Confederacy, their need to replenish their population with captives increased.