 Complete the following phrase:  The union of the country as Brittany occurred in 851 under King Erispoë, son of Nominoë, but was disrupted by disputes over succession and Norsemen incursions. Since 939, Brittany was re-established as a Sovereign Duchy with somewhat definite borders, administered by Dukes of Breton houses from 939 to 1166, before falling into the sphere of influence of the Plantagenets and then the Capets. The 