Leadership of which person was key to the north’s victory in the civil war?
lee
lincoln
seward
stowe
sumner

Lincolns Leadership was key to the North’s victory in the Civil War
As a commander in chief Lincoln was soon noted for vigorous measures, sometimes at odds with the Constitution and often at odds with the ideas of his military commanders. Lincoln tried throughout the war to keep the Republican party together and never consistently favored one faction in the party over another. 
Democrats accused Lincoln of being a tyrant because he proscribed civil liberties. Democrats exaggerated Lincoln's suppression of civil liberties, in part because wartime prosperity robbed them of economic issues and in part because Lincoln handled the slavery issue so skillfully. 
The Constitution protected slavery in peace, but in war, Lincoln came to believe, the commander in chief could abolish slavery as a military necessity. By 1864, Democrats and Republicans differed clearly in their platforms on the race issue: Lincoln's endorsed the 13TH Amendment to the Constitution abolishing slavery, whereas McClellan's pledged to return to the South the rights it had had in 1860.