Which of the following was a key factor in the Union's advantage during the Civil War?

The Union's significant industrial resources played a crucial role in providing it with a substantial advantage during the Civil War. The North had a well-established industrial base that allowed for the mass production of weapons, ammunition, and other military supplies. This industrial capability enabled the Union to equip and sustain its army more effectively than the Confederacy, which had limited industrial resources and faced challenges in production. Additionally, the Union's factories produced not only military equipment but also goods necessary for maintaining the civilian economy, which helped to support the war effort. This industrial strength was instrumental in the Union's ability to mobilize troops and resources, ultimately contributing to its victory in the war.

While factors like geography and international financial backing were relevant, they did not have the same level of impact on the Union's capacity to wage war effectively and sustain its efforts over the duration of the conflict. The size of the population also worked in favor of the Union, providing a larger pool of soldiers and laborers. However, it was primarily the Union's industrial strength that allowed for a more robust military infrastructure.