Memorizing chronological dates in Social Studies is notorious for high decay rates. The solution is two-sided retrieval cards.
The Cause-and-Consequence Card Format
Do not write cards that ask 'What happened in 1816 AD?'. Instead, ask 'Which treaty established the Mechi and Mahakali boundary rivers of Nepal, and what were its three key conditions?'. Binding dates to geographical and geopolitical consequences anchors memory.