The Ghosts of War series does not have a new book coming out soon. The latest book, Fallen in Fredericksburg (Book 4), was published in April 2016.
The first book in the Ghosts of War series, The Secret of Midway, was published in January 2015.
The Ghosts of War series primarily falls into the Historical genre. This middle grade series was written for ages 8-12, but can be enjoyed by older readers as well.