Start with high-confidence colonial & revolutionary ya books, then narrow by subgenre or adjacent topics.
Rifles for Watie
Harold Keith
Hamilton and Peggy!
L. M. Elliott
Across Five Aprils
Irene Hunt
The Letter Writer
Ann Rinaldi
Leigh Ann's Civil War
My Vicksburg
Miss Lizzie's War
Rosemary Agonito
Love & War
Melissa de la Cruz