The narrower and more specific the topic, the better. Preliminary research will be your friend here. Time spent on the front end here will make a better project. There are a few categories that you might consider: turning point battles, economic weapons and conditions, African American experience, women, technology, CHATTANOOGA, Lincoln, Southern interpretations, Legacy of the war.
As promised, here are some ideas for you to consider for Chattanooga...
Why Chattanooga? Investigation of the strategic importance of the town.
Economic importance of the area
The reason for Union victory at Lookout Mountain
Crossing the River
The Union bridges of the Tennessee
Conditions during the siege
Failure of artillery at Lookout Mountain and Missionary Ridge
General Thomas crests Missionary Ridge first
Sherman’s destructive forces amassed and trained in Chattanooga
The economic effect the war had on the city
Confederate or Union defense of the city