Short answers, pulled from the story.
The first mass draft into the Red Army occurred on the 17th of February 1918. This event marked a turning point during the Russian Civil War when the Soviet state needed to build its military forces quickly.
Organizers moved the celebration from Monday the 17th of February to Sunday the 23rd of February because that date fell on a Sunday in 1919. That choice of day has been retained ever since despite the original decree being published on the 18th of February 1918.
Vladimir Putin decreed it a state holiday in Russia in 2002 and renamed it Defender of the Fatherland Day. The name change reflected the new national identity after the USSR collapsed.
Ukraine never celebrated the 23rd of February as an official state holiday but instead established Defender of Ukraine Day on the 6th of December following a decree by Petro Poroshenko on the 14th of October 2014. Kazakhstan observes Defender of the Fatherland Day on the 7th of May marking the establishment of the Kazakh Armed Forces on the 7th of May 1992.
Kazakhstan celebrates the holiday on the 7th of May while Turkmenistan changed its celebration date to the 27th of January under President Gurbanguly Berdimuhamedow in 2009. Kyrgyzstan introduced the holiday through government decree on the 20th of January 2003 and holds parades in Bishkek.