Why you need railroads?
You need railroads because you will be able to transport your supplies that are needed to your troops faster than by horse and it be an advantage against your enemies.
Will the railroads help you?
Railroads will help you a whole lot with caring heavy supplies that your men are not capable of caring and you wont have to carry those heavy cannons around and have them slow you down.
How will this help you?
The railroads will help you big time you wont have to worry about your supplies running low and if it does all you have to is order more and it will be shipped to you. Railroads are also a great advantage against your enemies because they will not have this access like you do if you get railroads.
Why should you buy it?
The railroad is something that you can use even after the civil war is will make it easier to transport your good you will be able to reach more states than you have before . Also it is faster than taking a carriage or horse you economy will quickly grow with visitors coming and seeing your little community to see what you have to offer them.