Through attrition and massive advances on several fronts" is the correct answer. The main advantage of the North was that there were far more soldiers than in the South.
The north, also known as The Union, benefited from the fact that it controlled the vast majority of industrialized territories within the country This enabled it to exercise a naval blockade in 1861 during the civil war against the south or Confederacy.
This blockade aimed to cut the southern states' resources. As a response, the Confederacy ordered businessmen, who owned vast extensions of farming territory to shift their production to crops that would enable them to get access to food. However, the blockade would ultimately be decisive in the events that led to the defeat of the south.
