What significant event led to the creation of Denmark?

The correct choice highlights the significant role of Viking invasions in the formation of Denmark. During the late 8th century and into the 10th century, Scandinavian Vikings embarked on numerous raids across Europe, and this era was essential in the establishment of powerful tribal leaders and early kingdoms in the region that would later become Denmark.

The Viking Age was characterized by these seafaring warriors who settled in various territories, establishing trade routes, settlements, and political connections. This expansion facilitated not only the unification of Denmark as a distinct political entity but also helped create a sense of identity among the various tribes in the region. The influence of Viking culture, their social structures, and governance played a critical role in shaping the future of Denmark, firmly establishing it as a recognized kingdom.

In contrast, while the other events like Christianization, settlement from Germany, and the union with Norway are significant in Denmark's history, they came after the initial formation and consolidation of the state. Christianization integrated Denmark into the larger European culture and politics, while unions and settlements were responses to evolving political landscapes rather than the foundation of the nation itself.