 Complete the following phrase:  Compared to the agriculturally rich former capital Jolbon, Hwando was situated in a mountainous region with little arable land. To sustain the economy, Hwando had to constantly extract resources from the peoples in the countryside, which included the tribal communities of Okjeo and Ye. The Okjeo were said to have worked as virtual slaves to the Goguryeo king, hauling provisions such as cloth, fish, salt and other sea products from the peninsulas northeast to the Yalu basin, reflecting the arrangement that Goguryeo had to adopt after the entry of Gongsun Kang. By the 230s, Goguryeo had regathered their strength from these tributary relations and regained their presence in the Jolbon region. In 234, the Han dynastys successor state Cao Wei established friendly contact with Goguryeo, and in 238 an alliance between Wei and Goguryeo destroyed their common enemy Gongsun Yuan, the last of the Gongsun warlords See 