Complex sentence: Belle's son Charles Davinier, went on to serve in what was informally known as the Indian Army, although his service probably began with one of the territorial armies that existed before the formation of the British Indian Army in 1858.
Split into simpler sentences: Belle's son Charles Davinier, served in what was informally known as the Indian Army. His service probably began with one of the territorial armies that was founded before the formation of the British Indian Army in 1858.