Complex sentence: The battle forced the Visigoths to retreat to Septimania, which they continued to hold, while the success at Vouillé allowed the Franks to control the southwestern part of France and capture Toulouse.
Split into simpler sentences: The battle forced the Goths to retreat to Septimania, which they continued to hold. The success at Vouillé allowed the Franks to control the southwestern part of France, and capture Toulouse.