Final answer:
The North's three major advantages at the beginning of the Civil War were its larger population, superior industrial output, and extensive railroad network, providing significant manpower, manufacturing, and logistical benefits.
Step-by-step explanation:
At the beginning of the American Civil War, three major advantages that the North (Union) had were its larger population, greater industrial capabilities, and an extensive railroad grid.
The North's large population, estimated to be around 22 million people compared to the South's 9 million, provided a substantial manpower reserve. This allowed for larger armies and the ability to sustain losses more effectively. Additionally, the Industrial Revolution had significantly bolstered the North's industrial strength, with 1.3 million northerners working in factories compared to only 110,000 southerners, which meant that the North could outproduce the South in war materials on a massive scale.
Moreover, the North benefitted from an extensive and more efficient railroad system which was crucial for mobilizing troops and distributing supplies. This enabled the Union to maintain long supply lines, transport soldiers rapidly, and logistics that far exceeded Confederate capabilities. These strategic advantages were critical in the Union's ability to wage war.