Final answer:
Using the knowledge from 1861, the Union was likely to win the Civil War due to their superior resources, larger population, and the inability of the Confederacy to secure a swift victory or significant foreign support.
Step-by-step explanation:
If one had full knowledge of the conditions in 1861, it might have been logical to predict the Union would win the Civil War. Initially, both the Confederacy and the Union misjudged the resolve of their opponent, with the Confederacy expecting quick European support from nations like Great Britain and France, and the Union underestimating the Confederacy's will to fight for independence. However, the North's superior resources in terms of men and materials, and the Confederacy's need for a swift victory to stand any real chance, would suggest a Union advantage.
The critical factor that led to the Union's victory was its substantial industrial capacity and larger population. If the Confederacy could not secure a fast victory or significant foreign intervention, the prolonged conflict would increasingly favor the North. Lincoln's leadership and the Union's ability to mobilize and sustain a long war effort, with key victories like Sherman's capture of Atlanta, further secured the North's position. Over four years, what both sides initially thought would be a short conflict, resulted in a Northern victory in 1865.