The ruins of the Bhutia Basti fort near Yuksom are a reminder of Sikkim’s:

The correct answer is: a) Past conflicts with neighboring regions.

The Bhutia Basti fort was built in the 17th century by the Bhutia people, who were originally from Tibet. The fort was built to protect the Bhutia people from their enemies, the Lepchas. The fort was abandoned in the 18th century, after the Bhutia people were defeated by the Lepchas. The ruins of the fort are a reminder of the past conflicts between the Bhutia and Lepcha people.

The other options are incorrect because:

• b) Trade routes: The Bhutia Basti fort was not located on a major trade route.
• c) Mountainous terrain: The Bhutia Basti fort was located in a mountainous area, but this was not the reason for its construction.
• d) Early urban development: The Bhutia Basti fort was not an early urban development. It was a military fort.