Answer:
Step-by-step explanation:
Reasons.
They had a greater population pool to draw from.
They eventually promoted Grant and Sherman to leadership roles. They were the commanding officers that conquered the South. Up until that time the South had much better officers than the North.
The North had a better Navy. The could blockade the South's ports thus preventing them from selling their goods.
The North could manufacture weapons. As Rhett Butler says in "Gone With the Wind" the South will lose. They can't produce 1 cannon.
A very controversial point is that Lincoln promised to free the slaves. The Blacks joined the Northern forces as a result. This topic is well worth your time if you want something to study. It is very complex -- especially during Reconstruction.