Complex sentence: The province experienced a huge economic growth in the late 1930s, with a great urban development of Tripoli while Italian colonists cultivated lands (that had returned to native desert for many centuries) and improved Italian Libya's agriculture to international standards.
Split into simpler sentences: The province experienced a huge economic growth in the late 1930s, with a great urban development of Tripoli. In those years Italian colonists cultivated lands that had returned to native desert for many centuries, and improved Italian Libya's agriculture to international standards.