Cambodia was a farming area in the first and second millennia BC. States in the area engaged in trade in the Indian Ocean and exported rice surpluses. Complex irrigation systems were built in the 9th century. The French colonial period left the large feudal landholdings intact. Roads and a railway were built, and rubber, rice and corn grown. After independence Sihanouk pursued a policy of economic independence, securing aid and investment from a number of countries. Bombing during the Vietnam War damaged rice production. Lon Nol had a policy of liberalising the economy. This was followed by the victory of the Khmer Rouge and the emptying of the cities. After the defeat of the Khmer Rouge, a Five Year Plan was adopted, aiming to improve agriculture, industry and distribution, with a slogan of "export and thrift". Today, Cambodia remains a largely agricultural economy and industrial development is slow.