The history of this day goes back to 1922, when the Soviet leadership proposed to commemorate the fourth anniversary of the creation of the Red Army and the Red Navy. Although the decree on the organization of the two military branches was signed in January of 1918, it wasn't until February 23 when the first mass conscription of soldiers and volunteers began. The day was officially named Red Army Day.
The Red Army won the Russian Civil War against the White Movement, anti-Communist forces opposing the Great October Socialist Revolution of 1917, and later became known as the core of the Soviet Armed Forces.
Although the holiday was meant primarily as a tribute to war veterans and servicemen, February 23 is widely considered as Men's Day due to mandatory military service for all males. But in reality one doesn't need to serve in the army to celebrate the holiday, because the idea is that all men would stand up and defend their country when the time comes.