Why did the Unions win the American Civil War?

There are a number of schools of thought when it comes to answering the question of why the North won the Civil War. One of the more popular theories is that the North had a huge advantage when it came to both manpower and infrastructure. The North contained approximately 22 million people, compared to the South's relatively small 9 million. That advantage doesn't even include the black people who comprised almost 40% of the South's population, who weren't allowed to fight for the Confederacy but generally wanted to fight for the Union. Furthermore, the North had more than 5 times the number of factories the South had, allowing them to build more ships and blockade the South from recieving aid. Others argue that it was the Confedaracy's pro-slavery ideology which lost them the war, as it alienated a huge portion of their society as well as potential allies such as Britain, who had recently banned slavery. However, it is more likely that Britain's decision was based more on its need for Northern American industry rather than clashing moralities, again highlighting the importance of the North's infrastructure advantage. Another potential argument is that the leadership of the two sides was the key difference between them. Whilst it is true that Lincoln was renowned for his charisma and ability to inspire both sides of the political spectrum (in the North at least) and that Davis lacked these qualities, there is no sign of a loss of will amongst Confederate troops, or even those who stayed at home. Although the North didn't make much ground until Generals like Ulysses Grant took control, his main contribution was his willingness to sacrifice lives in order to take advantage of the Union's numerical superiority. Therefore, we can surmise that whilst other factors may have played a role, they were mainly only useful in terms of marshalling the North's superior manpower and industrial might.