Population and Immigration
A larger force has a significantly higher chance of winning against a smaller force. And while there are innumerable instances throughout history that challenges that idea, for the most part, if you go into a battle with more people, you’re going to have a higher chance of winning. So is it any surprise really that when you discover that the North had a significant population advantage over the South that the South had a problem keeping up? The North could afford to lose more people, could afford to send more soldiers to a particular area (even if they had lost that area in battle before), and they could perform in more theaters of war at once with more people than the South ever could.
In the North, the population in 1860 was nearly 22 million, while in the South it was merely 9 million. Of those 9 million, only 5 million or so were white. When you consider half of those numbers are female, you have a considerable advantage for the Union.
When we look at the numbers of actual fighting men, we see that advantage realized. During the duration of the war, the Union put forth 2,128,948 soldiers into battle. That number varies based on what source you look at. Some are closer to three million for the North, while others have closer to 1.8 million. For the South, numbers are also varied, but all point to their numbers coming in at about half of the Union’s fighting forces (anywhere between 750,000 and 1.2 million).
One of the reasons why the North had such a population advantage was that the vast majority of immigrants settled there. The numbers again vary depending on sources, ranging from 80 to 90 percent. When you consider that the majority of immigrants that did come into the South were slaves, it makes these numbers even less surprising.