Step 1: About Mahāvamsa.
The Mahāvamsa is a historical chronicle written in Pali, dealing with the history of Buddhism and rulers in Sri Lanka.
Step 2: Identification.
It provides detailed descriptions of Sri Lankan kings, dynasties, and the spread of Buddhism in the island.
Step 3: Analysis of options.
- (1) Sri Lanka: Correct, the Mahāvamsa is a chronicle of Sri Lanka.
- (2) Burma: Burmese history is recorded in different chronicles, not Mahāvamsa.
- (3) Thailand: Not connected to Mahāvamsa.
- (4) Cambodia: Cambodian history has its own chronicles.
Step 4: Conclusion.
Thus, Mahāvamsa describes the history of **Sri Lanka**.