Complex sentence: Having gained experience across Europe, the army arrived in Britain in late 865, landing in East Anglia under the command of Halfdan Ragnarsson and Ivar the Boneless, with the support of Ubbe Ragnarsson.
Split into simpler sentences: Having gained experience across Europe, the army arrived in Britain in late 865, landing in East Anglia. Under the command of Halfdan Ragnarsson and Ivar the Boneless, with the support of Ubbe Ragnarsson.