In 1949, the name of the War Department was changed to the Department of Defense. The absolute motives of the name change are irrelevant to this request. However, the consequences of the name change are relevant.
The use of the term Defense implies that it is a department concerned with the defense of Our nation. This is anything but the actual case. Since 1949, America has only once been under the threat of imminent attack yet the U.S. Central Government has conducted several wars of aggression against various countries - many of which were third world countries that posed little if any threat to U.S. sovereignty. This is inconsistent with the name - Defense Department. On the other hand, the name - War Department - does not specify the offensive or defensive nature of conflicts