Complex sentence: So the rescued child was placed under the protection of King Inge Bårdsson, after whose death in 1217 he, at the age of 13, was chosen king against the candidacy of Inge's half-brother, earl Skule Bårdsson.
Split into simpler sentences: So the rescued child was placed under the protection of King Inge Bårdsson. Håkon was chosen against the candidacy of Inge's half-brother, earl Skule Bårdsson.