Complex sentence: Another source of income came from many residents who became mercenary officers: so many officers from Mollis made their fortunes in foreign military service that the village became known as an "Aristocrats' Nest".
Split into simpler sentences: Another source of income for the village came from many residents who became mercenary officers. So many officers from Mollis made their fortunes in foreign military service that the village became known as an "Aristocrats' Nest".