war zone

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An area in which military combat takes place.
• noun An area at sea in which ships are prone to being attacked during a war.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A region where war is ongoing.
• noun A region where structures are damaged or in disarray, appearing similar to the effects of a military conflict.
• noun By extension, any area with a significant display of damage or disarray.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a combat zone where military operations are coordinated (especially a designated area in international waters where the rights of neutrals are not respected by nations at war)