Final answer:
Louisburg was called the Gibraltar of North America due to its strategic value and similarities with the fortress of the same name in Spain.
Step-by-step explanation:
According to the information provided in the questions, Louisburg was called the Gibraltar of North America. The term 'Gibraltar' refers to a fortress located on the southern coast of Spain, which is known for its strategic position and military significance. Similarly, Louisburg was a heavily fortified town in Nova Scotia, Canada, which served as a significant military stronghold during the 18th century. Its defensive structures and importance in controlling access to North America made it comparable to Gibraltar in terms of its strategic value.