You're mischaracterizing what's been happening in Ukraine for the last 12-18 months. We've been hearing that Russia's economy is failing for almost three years. Ukraine devoted its best troops and equipment to the 2023 summer offensive that failed. Ukraine is at a disadvantage because Ukraine has less manpower, very little industrial capacity and is completely reliant on foreign aid, not because Biden was tying hands behind their back. Not conscripting 18-25 year old men is a Ukrainian decision.
For your education, this is what the NYT thinks-
https://www.nytimes.com/2025/01/23/world/europe/ukraine-russia-soldiers-loss.html
1863- A lot happened that year. You said Lee advancing into Pennsylvania. The Army of Northern Virginia started moving northward in early June 1863. The Battle of Gettysburg started July 1, 1863. Grant and Farragut were cutting the south in two. Vicksburg started in May of 1863, and ended in July. Shiloh was already a Union victory. The Union had big industrial and manpower advantages. The Confederacy was trying to force a decisive battle while it still could. Ukraine does not have industrial or manpower advantages, and has been getting steadily pushed back for 12-18 months. The US Civil War was a civil war, the USA was not backing one side as a proxy.
Early 1944- The Allies were winning. The Soviet Union had been steadily advancing on the Eastern front since Stalingrad, Germany's counteroffensive at Kursk failed. Germany evacuated North Africa, the Allies liberated Sicily, and were moving north up the Italian peninsula. In the Pacific, the Allies steadily advanced and the Japanese steadily retreated since Guadalcanal ended in February of 1943, and had lost aircraft carriers it could not replace at Midway in early June of 1942. The Allies industrial and manpower advantages were taking hold. Again, Ukraine does not have those advantages.
For Korea- That's a really terrible analogy. You're comparing North Korea versus the United Nations lead by the US, to Russia versus Ukraine. Does the United States have an invasion fleet heading for, I don't know what the analogy would be, Sevastopol right now and tens of thousands of troops headed for Odesa?
Please indulge me- How is Ukraine going to turn things around?