Glorious Mood-Setting Music of Russian Proletariat (if you want to skip straight to the national anthem, it's at 57 minutes)
A Red Star Over Warsaw: A Tale of Soviet Glory(1)
Mikhail Tukhachevsky, the "Red Napoleon"
"There can be no doubt that if we had been victorious on the Vistula, the revolutionary fires would have reached the entire continent."
--Attributed to Mikhail Tukhachevsky
July 5, 1920: The Battle of Lvov
A small hill across the river from Lvov bore on its crest two cavalrymen, one sweating in the hot July sun and the other entirely unruffled by the heat. This second, his face ornamented by a huge and bushy black mustache, grinned, looking up at the cloudless sky. "Sergei, my boy, we have chosen a good day to arrive in this city! The earth will be firm and hard, perfect." The tall, grim Tatar on his right nodded, wiping sweat from his brow. "Sir, my scouts tell me that the Poles within the city lack ammunition and much necessary weaponry, including machineguns. If we attack today, we will crush them with little difficulty." Semyon Budyonny's face hardened, and he glared at Sergei. "I did not ask for your tactical assessment, boy, only information. Remember your place." They might be fighting for the Soviet Union, but Budyonny's Cavalry Army was very much a hierarchical beast. Budyonny's face softened slightly. "However, you make a good point. Tell the men to form up. We will charge them." Sergei raised an eyebrow. "A charge? But is this not suicide, even with them lacking machineguns?" Budyonny laughed. "What is glory without risk, my boy? This day will be remembered as the last great cavalry charge, I tell you that. And as a great victory, to boot." Sergei, repressing a sigh, nodded, and kicked his horse in the sides, riding off to where the men waited. Budyonny returned his gaze to the city, humming a folk song under his breath. This would be his day, not Stalin's. The Georgian had thrown away his chance at glory when he had decided 'supplies' were more important than victory(2).
* * *
The Polish corporal watched his men pile sandbags one on top of the other, supplementing any holes with bricks and tiles ripped from the streets themselves. It was too soon, much too soon. Had the Cossacks(3) arrived a month later, when the promised supplies from Warsaw had arrived, Lvov might stand a chance. As it was, not only were the fighting mieszczuchy(4) outnumbered, they were outgunned; many of his men were armed with pitchforks and rakes, shovels and the occasional elder sword plundered from some rich man's mansion. Not only that, but with the vast majority of men being drafted and sent away from their home city, most of the men he had left were old, ancient in some cases. The median age was above forty, and there were more than a few over fifty and sixty, some of whom could barely walk as it was. His reverie was interrupted by one of these very men, an elderly veteran, scurried up to him as fast he could. "Sir! The Russians are approaching!" The corporal was filled with an uneasy and growing panic as he rushed to the barricade, covering his eyes with a hand to block the sun. They seemed endless, the Cossacks. Legions of horse, supplemented by barely-seen sharpshooters on the few trees and hills across the Bug. They were coming towards the city at an awfully quick pace. He turned to the man who had told him. "Get to the other barricades as quickly as possible and tell them to be ready. The Russians are coming." The man nodded and was off. The corporal yelled, "Prepare weapons!" and began firing himself at the Russian line, not seeming to make a discernible impact. They crossed the river and did not seem to slow. He was puzzled. Would they not dismount? They were two hundred meters away and not slowing. What fools would charge defensive emplacements? One hundred meters. Finally, he realized what was happening, and screamed; "Fix bayonets!" It was too late. As he was halfway through screwing on his own, the first few Cossacks leapt over the barricade, crashing onto its defenders. Screams rang out along the line, and the corporal found himself surrounded by thick bodies, unable to see beyond the nearest enemy. He kept firing, blindly, into the mass, until a bayonet stabbed forth from a man seated on a horse nearby; tall and thin, with a grim look on his face. That was all the corporal had time to register before the bayonet struck him in the eye and, after an explosion of pain, the world became dark. (3)
Notes
(1) This TL is going to be unabashedly pro-Soviet. Just be ready for that. It's not gonna be all flowers and joy though.
(2) IOTL, the cavalry army and Stalin's forces were slowed by weather; here, however, the weather is much better, allowing the cavalry army to reach Lvov nearly a month earlier. Stalin, meanwhile, is going slow as a snail, as per usual. Since they're so much earlier, the Poles have less than half of the supplies they had IOTL and are nowhere near ready for a battle.
(3) And so it begins! Next bit will be on the Battle of Warsaw.
* * *
My new TL! Basically, the Soviets win the Polish-Soviet War, though not without some difficulties. This is just a bit of a snippet to start off.

Do comment and criticize!