In 1902 Abd al-Aziz Ibn SAUD captured Riyadh and set out on a 30-year campaign to unify the Arabian Peninsula. In the 1930s, the discovery of oil transformed the country. Following Iraq's invasion of Kuwait in 1990, Saudi Arabia accepted the Kuwaiti royal family and 400,000 refugees while allowing Western and Arab troops to deploy on its soil for the liberation of Kuwait the following year. A burgeoning population, aquifer depletion, and an economy largely dependent on petroleum output and prices are all major governmental concerns.