Short answers, pulled from the story.
The Dnieper-Carpathian offensive was a major Soviet strategic operation fought from late December 1943 to early May 1944 on the Eastern Front of World War II. It involved Soviet forces from the 1st, 2nd, 3rd, and 4th Ukrainian Fronts fighting against German Army Group South and Army Group A across a 1,200-kilometer front. The goal was to clear Axis forces from most of Ukraine and Moldova and split Army Group South in two.
Nearly 3,500,000 troops from both sides participated in the Dnieper-Carpathian offensive. At the start of January 1944, the four Soviet Ukrainian Fronts alone fielded 169 rifle divisions, 9 cavalry divisions, 18 tank and mechanized corps, 31,530 guns and mortars, 1,908 tanks, and 2,364 combat aircraft.
The Korsun Pocket, also called Little Stalingrad, was an encirclement completed on the 28th of January 1944 when Soviet forces trapped roughly 60,000 Germans from the XI and XXXXII Army Corps near Korsun. When the trapped force attempted a final breakout on the night of the 16th-the 17th of February, the Soviets took approximately 15,000 prisoners and killed at least 10,000 Germans, including the pocket's commander Wilhelm Stemmermann.
Hitler dismissed Erich von Manstein and Ewald von Kleist on the 5th of April 1944 after blaming them for the overall strategic collapse of the German position in Ukraine. He replaced them with Walther Model and Ferdinand Schörner respectively, and renamed Army Group South to Army Group North Ukraine and Army Group A to Army Group South Ukraine. The offensive marked the end of Manstein's career in the Wehrmacht.
The offensive forced the German high command to transfer 34 divisions totaling 550,000 men and 853 tanks and assault guns from France, Germany, and other fronts to Ukraine between January and May 1944. By the 6th of June 1944, German forces in France had been stripped of 45,827 troops and 363 tanks, assault guns, and self-propelled guns as a direct result of the fighting in Ukraine, critically weakening the forces available to resist the Allied landings.
The unusually warm winter of 1943-1944 turned Ukrainian roads into rivers of mud, often two feet deep, severely limiting German mobility while Soviet tracked vehicles maintained their advance. British correspondent Alexander Werth, traveling with the 2nd Ukrainian Front, observed that most German tanks could not cope with conditions that the Soviet T-34 managed. The spring mud, known as rasputitsa, also flooded rivers like the Gniloy Tikich, which trapped German forces attempting to break out of the Korsun Pocket in February 1944.