A narrative I hear a lot in military history is that Cavalry just stopped being used during WW1, due to advances in technology. Yet the image I get of the Russian Civil War, and of the Polish-Soviet war through books like Babel's Red Cavalry, is that cavalry was still used extensively: is this true? If so, just how effective were cavalry units? What kind of roles did they fill? Were they used on the front-lines? And when and why did the Soviet army eventually mechanise?
First of all, while most people think of World War I as the "end of cavalry," in reality cavalry still retained many uses in modern combat. /u/DuxBelisarius had dealt with this topic in depth, here is one answer of his among many. Also: https://www.reddit.com/r/AskHistorians/comments/50dh9l/how_common_were_cavalry_charges_in_ww1/
In short, cavalry tactics advanced along with new technology, and cavalry adapted to a new niche on the battlefield, even though it may not have been as decisive as it once was.
On the Eastern Front, and in the Russian Civil War, cavalry retained paramount importance because of the huge distances covered. When a hole opened up in the front line, cavalry could dash through and cover hundreds of miles, wreaking havoc behind enemy lines. Simple mobility made cavalry very valuable.
However, "cavalry" does not imply that they only fought from horseback. The term more loosely implied that soldiers traveled on horseback, and could fight from it, or more likely, fight as mounted infantrymen, mounting to move and dismounting to shoot. The Reds proved more effective at this than the Whites, emphasizing firepower over traditional lance-and-sabre charges. The Red Army's First Cavalry Army was a particularly good unit when it came to this (I think Babel was a member.) On the battlefield, you would see thinkgs like the tachanka, a horse-drawn cart with a machine-gun in it. https://s-media-cache-ak0.pinimg.com/736x/b8/38/09/b838094fa6065a2eb56325a204e06fbe.jpg
