Beginning in the 1900s, Iquitos became wealthy through its rubber industry throughout the rubber boom; it attracted thousands of immigrants from around the world, mostly young single men who hoped to make their fortunes in rubber. The rise of the automobile and related industries had dramatically increased the worldwide demand for rubber. Some men became merchants and bankers, and made their fortunes that way. Many of the European men married indigenous women and stayed in Peru the rest of their lives, founding ethnically mixed families. The immigrants brought European clothing styles, music, architecture and other cultural elements to Iquitos. They established an opera house that featured European classical music.