Complex sentence: The Swedish queen Yrsa gave them a large Swedish army headed by Vogg, who seize the wicked elf queen by surprise, just as she had suddenly attacked the king, tying her arms so she could not use her magic arts.
Split into simpler sentences: The Swedish queen Yrsa gave them a large Swedish army headed by Vogg. They seize the wicked elf queen by surprise, just as she had suddenly attacked the king, tying her arms so she could not use her magic arts.