Needs a Better Title
Soldiers often come up with a name for the enemy that's easy to remember, usually quicker to say than their actual name. Sometimes this is a racial or ethnic slur; sometimes it's a cultural reference, and sometimes refers to appearance. Doing so is commonly a form of Demonization
and has the effect of 'Othering' the enemy, making them seem less human, thus keeping the troops from considering the enemy's humanity
, and thus making it easier for the troops to kill them. For that reason, the practice is often encouraged (or at least not discouraged) by the troops' superiors while the war's going on. In science fiction or fantasy settings, this is made even easier when the enemy is not the same race as the troops
These designations often find a way into propaganda and slogans used to whip up civilian support for the war effort, and continued use of these terms after the war can indicate a person who lived through the war and either adopted the term as a habit of speech or is having trouble moving past those years.
Compare to Demonization
, What Measure Is a Mook?