Complex sentence: Alexander Biddle (1819-1899) was a Union officer that fought under Abner Doubleday in the Battle of Gettysburg and also at the battles of Fredericksburg and Chancellorsville.
Split into simpler sentences: Alexander Biddle (1819-1899) was a Union officer that led soldiers under Abner Doubleday at the Battle of Gettysburg. He also fought at the battles of Fredericksburg and Chancellorsville.