Complex sentence: Haakon claimed half the kingdom, and was proclaimed king at Øyrating in Nidaros in late 1093, taking control of the part of the kingdom once held by his father, also including the Frostating of Hålogaland, the Gulating and the Upplands.
Split into simpler sentences: Haakon claimed half the kingdom for himself, and was proclaimed king at Øyrating in Nidaros in late 1093. He thereafter took control over the part of the kingdom once held by his father, which also included the Frostating of Hålogaland, the Gulating and the Upplands.