Starting in the 1730s, French engineers constructed complex irrigation systems to increase sugarcane production. By the 1740s Saint-Domingue, together with the British colony of Jamaica, had become the main supplier of the world's sugar. Production of sugar depended on extensive manual labor provided by enslaved Africans. An average of 600 ships engaged every year in shipping products from Saint-Domingue to Bordeaux, and the value of the colony's crops and goods was almost equal in value to all of the products shipped from the Thirteen Colonies to Great Britain. The livelihood of 1 million of the approximately 25 million people who lived in the France in 1789 depended directly upon the agricultural imports from Saint-Domingue, and several million indirectly depended upon trade from the colony to maintain their standard of living. Saint-Domingue was the most profitable French colony in the world, indeed one of the most profitable of all the European colonies in the 18th century.