Complex sentence: He joined the British Army in 1802 and served with distinction in India, Spain, and France, until family circumstances forced him to sell his commission in 1820, though he was later referred to as "Captain Cargill".
Split into simpler sentences: He joined the British Army in 1802 and served with distinction in India, Spain, and France. Family circumstances forced him to sell his commission in 1820, though he was later referred to as "Captain Cargill".