Complex sentence: They conquered and colonized parts of Britain during the 8th and 9th centuries A.D. The 2nd invasion was by the Normans of the 11th century, who spoke Old Norman and eventually developed an English form thereof called Anglo-Norman.
Split into simpler sentences: They conquered and colonised parts of Britain during the 8th and 9th centuries AD. The second invasion was by the Normans of the 11th century, who spoke Old Norman and eventually developed an English form of this, called Anglo-Norman.