Complex sentence: Caipre Gabra was absorbed into the larger Annaly kingdom, so named after "" the great-grandfather of Fearghail O'Farrell, which in turn became known as Longphoirt, now Longford, after the O'Farrell's fortress of the same name.
Split into simpler sentences: Caipre Gabra was absorbed into the larger Annaly kingdom (approximately county Longford), named after "" the great-grandfather of Fearghail O'Farrell. Annaly eventually became known as Longphoirt, now Longford, after the O'Farrell's fortress of the same name.