PS
My main errors in the first game were probably these:
The assumption that I could actually hold the line from Kiev to Odessa.
The assumption that even after withdrawing from the east, i would have enough industry left in the west and center to continue "building up my army", rather than just spending all my IC on supplies and reinforcements and not really getting anywhere. BTW throughout the entire war Galicia/WUPR build like 1 or 2 new divisions.
Not realizing that I could keep Poland neutral longer than historical if the conditions are right
Not realizing how much damage the Polish-Soviet non-aggression agreement would do to me
Some tactical errors made throughout the war particularly in the crucial months of mid 1919, which I mostly wasted on trying to destroy a group of surrounded Soviet forces, wheras what I should have been doing is recovering my eastern provinces at any cost
So here's a quick rundown of my followup game of Ukraine and some things that i did differently:
-During the initial chaos after independence, I tried to make sure that less of my IC-bearing provinces would get occupied, because even if I liberate them later, there's quite a lengthy recovery period.
-I helped Germany last a couple of extra weeks, which actually appears to have made some positive difference in helping me be more prepared for the war. Germany surrendered in mid December.
-I decided to play nice with Poland after all, I can't afford to get wrecked by Poles and Soviets when they make non-aggression pact with each other. Instead, I tried to end the war with Poland as quickly as I could and then manage the fallout from that.
-Maybe a bit gamey, but since Poland grants me access to their territory after making peace, and stationing units in Polish territory means Poland is taking care of supplying them, I decided to send some of my most useless militia divisions to hang out in Poland temporarily and let the Poles take care of feeding them for a while until the time when my morale recovers enough for them to actually become useful again. Meanwhile i can make use of the freed up resources and try to build more units.
-Ending the war with Poland early allowed me to establish a somewhat defensible line on the Dnieper that lasted until the end of the first phase of the Soviet invasion. When the anti-Soviet Grigoriev revolt happened and Makhno also briefly joined my side, i was able to use their help to expand my territory to the right side of the Dnieper river and start recoving Donbass where most of my industry is located.
-Since we recovered Zaporozhye and Mariupol, the event for Makhno's surprise attack against Denikin did not fire, allowing me to maintain my de-facto alliance with Makhno for another 9 months or so, which was of great value to me. Historically this probably would not have happened as Makhno would have probably felt sufficiently threatened by Petliura that he would have still turned on him at the very first opportunity, but hey, I'll take it. Ultimately he still turned on me of course.
-Once Denikin's army started running out of steam and collapsing by early 1920, I was able to inch my way further to the east and even take Rostov, which was the key objective in making sure that Kuban defects to me
So on April 6th, Kuban defected.
Later in April, Crimea defected as well. Both became my allies.
Holding on to East Ukraine made a crucial difference in allowing me to actually continue mobilizing more units for the fight. That and the addition of troops from Crimea and Kuban allowed me to even briefly encircle and destroy some Soviet units which definitely helped in the long term, but unfortunately it was not enough to make Soviet Russia surrender.
On the other hand, my advantage was upset by Makhno's eventual defection, then the Polish re-entry into in late 1920, and finally Soviet Russia's victory against most of the remaining White Russian forces. Ultimately I had to abandon many of my gains and even withdraw from Kharkov and most of the left-bank Ukraine in general.
This is the line that I had to fall back to and defend with tooth and nail. Any further retreat would have meant serious and probably irrecoverable losses. As you can see, here the Soviets are in the midst of crushing the Tambow and West Siberian peasant rebellions, which gave me a short breathing room to establish a defensible line in the Caucasus, but didn't give me much advantage other than that.
Three more years passed by since that time, which I had spent mostly fighting off enemy attacks while hanging on to defensible positions and simultaneously trying to build up more forces and bring down my dissent. At some point the Soviets gave up the fight against Poland, which made things worse for me again. This was the most difficult and gruesome part of the war, the Eastern version of WW1 trench warfare. At one point, Crimea simply ran out of manpower and requested annexation. This isn't how annexation is normally supposed to happen, rather this is one of the general events I made a long time back called "preemptive annexation" that is triggerable for all countries and is intended to help avoid certain game-breaking outcomes. Basically, when certain conditions are met, a country can (and if it is led by AI, it will) request annexation by its larger allies or masters. The primary condition is if it has been reduced to 1 VP or one province (meaning that if it is not annexed by its ally, it is risking being annexed by a hostile power and losing all of its units and manpower in the process - which is wrong in my opinion).
Another alternative condition is if it has a huge army but very low IC, which means it is not going to be able to properly supply or reinforce this army even if it has manpower reserves left. If that happens, it is easily exploitable and is basically doomed to failure unless a larger ally takes control of it and takes responsibility for supplying this army.
One more possible condition is if doesn't have any manpower left to continue reinforcing its units and it had reached its maximum level of mobilization at the same time. In this case, if it is not annexed, all of its units will gradually reach zero strength and become worse than useless, they will become a burden since AI doesn't know how to handle them properly, also all of that country's IC is completely going to waste whereas it could be contributing to its allies war effort. This is the case for Crimea - give the constant state of warfare since 1914, when it secedes from South Russia it doesn't have that many reserves left to count on in the first place, particularly since it doesn't have cores on all of its the provinces but only the ones with majority Tatar and Ukrainian population, and the constant bloody battles against Soviet Russia and Poland since independence had further bled them dry until they finally agreed to annexation by Ukraine.
By 1924/1925, the Soviet dissent finally started reaching such levels that their army became only half-way functional and constantly distracted by revolts elsewhere. This allowed me to go on offensive and slowly start pushing them back, until in late September 1925 they sued for peace. This is a screenshot of the situation shortly before peace was finally made.
Poland, by that point, was already stuck in a stalemated war against Sweden and its Baltic allies, and its dissent had also reached pretty catastrophic levels, so once I brought fresh units from the Eastern front to the West, Poland's fate was sealed in that conflict.
Galicia was mostly liberated by mid 1926.
Finally with the Ukrainian forces on the doorstep on Warsaw and Krakow, Poland surrendered. West Ukraine and Kuban was annexed shortly afterwards.
Many many Ukrainians died to achieve this outcome, but in the end, we were triumphant.
(this was still on normal difficulty btw lol)