Complex sentence: Montalembert's father, Marc René, had fought under Condé, and subsequently served in the English army; he married Elise Rosee Forbes, and his eldest son, Charles, was born in London.
Split into simpler sentences: Montalembert's father, Marc René, had fought under Condé, and subsequently served in the English army. He married Elise Rosee Forbes, and his eldest son, Charles, was born in London.