勿忘国耻 (勿忘國恥) wù wàng guó chǐ

wù wàng guó chǐ proper noun Never forget national humiliation
Domain: Modern Chinese 现代汉语
Notes: Refers to Mukden railway incident of 18th September 1931 九一八事变 and subsequent Japanese annexation of Manchuria (CC-CEDICT '勿忘國恥')