Complex sentence: Juan Bautista Rondeau (1735--1813) was a French military, in service of the Spanish crown during the Viceroyalty of Peru and Viceroyalty of the Rio de la Plata.
Split into simpler sentences: Juan Bautista Rondeau (1735--1813) was a French military, in service of the Spanish crown. He served during the Viceroyalty of Peru and Viceroyalty of the Rio de la Plata.