Jingkang Incident
All subsequent emperors of the Northern Song were his descendants, as well as the first emperor of the Southern Song. However, from Emperor Xiaozong onwards, subsequent emperors were descendants of his brother, Emperor Taizu. This largely stemmed from the Jingkang Incident, whereby most of Emperor Taizong's descendants were abducted by the Jurchen-led Jin dynasty, forcing Emperor Gaozong to seek a successor among Taizu's descendants, as Gaozong's only son had died young.