Final answer:
The flag of Belarus was modified by adding a shield in 1992 to distinguish it from the Russian tricolor flag.
Step-by-step explanation:
The nation whose flag had a shield added in 1992 to distinguish it from the Russian tricolor flag is Belarus. Belarus declared its independence from the Soviet Union in 1991, but unlike Latvia, Estonia, and Lithuania, it did not seek to distance itself significantly from Russian influence. The flags of Estonia, Latvia, and Lithuania do not resemble the Russian flag and thus did not require a change to distinguish them.
However, the flag of Belarus was similar to that of Russia, and the addition of the shield was to add a distinctive feature. This shield comprises a red star, a map of Belarus, wheat ears, and other symbols that represent the cultural heritage and values of the nation.