The southern Chinese dynasty of Liu Song, which was feuding with Northern Wei, encouraged both Northern Yan and Goguryeo to oppose Northern Wei. However, Liu Song's plan did not work out, as Goguryeo imprisoned the emperor of Northern Yan in 438. The Liu Song court was outraged and warned Jangsu that the death of the Northern Yan ruler would lead to war. However, Jangsu ignored the threat and executed him, bringing the short-lived Northern Yan dynasty to an end. Liu Song troops then attacked Goguryeo but were easily defeated. Peace resumed in the following year when Jangsu sent 800 horses as a gift to the Liu Song emperor, to aid him in his ongoing war against Northern Wei, allowing Goguryeo to concentrate its forces against Baekje and Silla to the south while Liu Song and Northern Wei were occupied against each other to the west. Jangsu again encouraged Liu Song to invade Northern Wei in 459 when he sent loads of crossbows and provided gold and silver. The Northern Wei government was upset by Jangsu's actions but had to keep peace with Goguryeo to continue its war against Liu Song and the Rouran Khaganate.