Complex sentence: Some sources such as Sin's "Joseon Sangosa" claim that Taizong was forced into the outskirts of Beijing, but Sin's account has been challenged on the basis that it lacked support in traditional Korean and Chinese sources.
Split into simpler sentences: Some sources such as Sin's "Joseon Sangosa" claim that Taizong was forced into the outskirts of Beijing. However Sin's account has been challenged on the basis that it lacked support in traditional Korean and Chinese sources.