The term "Fall Line" is not heard much today. It was a term used much more in the 18th and 19th century. It was basically where the water collected inland would fall back at its greatest power in its return to the sea. It lead to several areas getting names that matched its importance. One place that comes to mind was Fall River, Massachusetts. This was an area that had a great deal of industry as the water was very strong here and the factories could take advantage of the water power.
Remember in the mid 19th century water was still the most used method of power for factories. In these places they would build massive water wheels to make the most of the waters power.The Fall line ran close to the coast of Massachusetts, Connecticut, New York, New Jersey. This would be the areas of the greatest manufacturing in the United States. It would be one of the reasons why the north was always the industrial part of the nation. The Fall Line allowed materials to be made and since they were close to the coast, shipped to where ever needed. It was one of the greatest weapons of the north.
In Lincoln's own words he knew how important the Fall Line was. Saying that it was only a matter of arithmetic that the north would win the war due to the great industry provided by the Fall Line.
Often in the talk of the Civil War we mention many things, but we so often forget that item that was always in the back of Lincoln's mind...The Fall Line. He knew that it would help to win the war and it did!