During Yangwon's reign, Goguryeo gradually grew weaker and was obliged to take various urgent measures to block foreign invasions, eventually losing the Seoul region to the alliance of the other two Korean kingdoms.
In 548, he sent 6,000 soldiers against Baekje's Doksan Fortress but the Silla general Ju Jin led a relief army and the Goguryeo assault failed.
When Yongwon's court refused, Cui Liu became furious and punched Yangwon off his chair.
[dubious – discuss][citation needed] In 557, Yangwon designated the prince Go Yang-seong as heir to the throne.
In the tenth lunar month of that same year, the commander Gan Juri of Hwando fortress rebelled, but the rebellion was put down and he was executed.