With the country's emphasis on trade and economic growth, Song China's economy began to use machines to manufacture goods and coal as a source of energy. The advances of the Song in the 11th/12th centuries have been considered an early industrial revolution. Economic advancements came at the cost of military affairs and the Song became open to invasions from the north. China became divided as Song's northern lands were conquered by the Jurchen people. By 1200 there were five Chinese kingdoms stretching from modern day Turkestan to the Sea of Japan including the Western Liao, Western Xia, Jin, Southern Song and Dali. Because these states competed with each other they all were eventually annexed by the rising Mongol Empire before 1279.