Complex sentence: Theodore Ayrault Dodge (May 28,1842--1909) was a Union officer in the American Civil War and a military historian of both that war and of the great generals of ancient and European history.
Split into simpler sentences: Theodore Ayrault Dodge (May 28,1842--1909) was an American officer and military historian. Hoe fought as Union officer in the American Civil War; as a writer, he devoted to both Civil War and of the great generals of ancient and European history.