Complex sentence: In the 910s Gwent acknowledged the lordship of Wessex, and Deheubarth and Gwynedd acknowledged that of Æthelflæd of Mercia; after Edward's takeover of Mercia, they transferred their allegiance to him.
Split into simpler sentences: In the 910s Gwent acknowledged the lordship of Wessex, and Deheubarth and Gwynedd that of Æthelflæd of Mercia. After Edward's takeover of Mercia, they transferred their allegiance to him.