How did the advantages of the north at he start of the war continue to be advantages?

Answer 1

The chief advantage was simply a much bigger population from which to recruit armies. When Grant became General-in-Chief, he ended the system of prisoner-exchange, knowing that the Confederates would run out of men first. So that advantage steadily mounted-up.

Another was the much greater railroad mileage in the North, and the capacity to move troops and supplies by rail. Again, as the Union armies began to destroy Southern railroads, the disparity in rail mileage widened further.

Answer 2

The North had several advantages at the start of the war, including a larger population, a more developed industrial base, and more extensive transportation networks. These advantages continued to be advantages throughout the war as the North was able to mobilize more troops and resources, produce more weapons and supplies, and maintain better communication and supply lines. Additionally, the North's control of the seas allowed them to blockade Southern ports, cutting off crucial trade routes and weakening the Southern economy.