The Armies of Darkness is a compound wording for the German Army (Wehrmacht). It is just like the expression "Nazi Army" a word to "strengthen" the evilness and the badness of the German soldiers.
A sarcastic or mocking description of the number of people or things one is dealing with. Usually followed by either a single or two digit number. This is more often said after being raged at by other people who complain how many more allies you have than them, usually when your numbers are much lower than what they accused you of having, to show them how stupid they sound.
Armies are the plural noun of arms. Derived from the latin word Brachium meaning the upper segment of the arm or forelimb extending from the shoulder to the elbow.
Armies holds some of the larger upper body muscles and are particularly expanded in men as they have a high amount of testosterone which helps build muscle strength in order to flex on the ladies and get some sweet puss. This serves the purpose of procreation and protecting ones children during aggravated disputes against other males.