The Great Depression harmed Kuwait's economy, starting in the late 1920s. International trading was one of Kuwait's main sources of income before oil. Kuwaiti merchants were mostly intermediary merchants. As a result of the decline of European demand for goods from India and Africa, Kuwait's economy suffered. The decline in international trade resulted in an increase in gold smuggling by Kuwaiti ships to India. Some Kuwaiti merchant families became rich from this smuggling. Kuwait's pearl industry also collapsed as a result of the worldwide economic depression. At its height, Kuwait's pearl industry had led the world's luxury market, regularly sending out between 750 and 800 ships to meet the European elite's desire for pearls. During the economic depression, luxuries like pearls were in little demand. The Japanese invention of cultured pearls also contributed to the collapse of Kuwait's pearl industry.