This is such a simplistic view of the war. The civil war started because the country already had internal fault lines, and was pulled in different directions by Russian and Western meddling until it broke. The invasion was just the latest in a series of escalations. Nothing about this war is in the interest of the people living on the battlefield, they got duped or forced into fighting each other. Encouraging them to fight on is messed up.

Edit: I'd also like to add that Russia seemed quite willing, prior to the invasion, to have a compromise in which Ukraine would be neutral. The US especially clearly wasn't interested, insisting instead on its own supremacy, in which no opposing or neutral countries are to be tolerated. To this end they also supported the worst elements of Ukrainian society, ultra-nationalist Banderites, which they had been doing since the end of WW2.