Complex sentence: Teniente-Coronel George Thompson (1839-1876) was an English engineer, was in charge of the Paraguayan military engineering in the Paraguayan War, and was the author of an important primary source on its history.
Split into simpler sentences: Teniente-Coronel George Thompson (1839-1876) was an English engineer, AND was in charge of the Paraguayan military engineering in the Paraguayan War. He was the author of an important primary source on its history.