Nice quiz, and I know it makes sense, but I still find it a bit odd to say that Russia gained independence from the USSR as it was basically just a reformed Russian Empire. Also, Vietnam and Yemen becoming independent when two parts of the country united feels weird as "becoming independent" to me means that previously they were under foreign rule, whereas Yemenites and Vietnamese had been ruling themselves for decades.
Vietnam declared its independence in 1945, it was divided in 1954, and then reunified in 1976.