Final answer:
The material provided does not directly answer the question about who challenged the warriors when the ship arrived in Denmark. Instead, it discusses the historical context of Norse exploration and other European historical events.
Step-by-step explanation:
When the ship arrived in Denmark, the reference material does not mention any specific challenge to the warriors. The Norse explorers, including Leif Ericson and his father Eric the Red, are known for their voyages of discovery from Greenland to North America, predating Christopher Columbus by hundreds of years. The material provided covers various historical accounts of Norse exploration, the creation of New Sweden by the Swedes in defiance of Dutch trading monopolies, and examples of European conflict such as Napoleon's demands upon Denmark. However, the challenge upon arriving in Denmark is not directly addressed in the provided excerpts.