Final answer:
The Pripyat River, flowing eastward and a major tributary of the Dnieper, is located in Ukraine. It is historically linked to the Chernobyl Disaster and the territorial changes during the reign of Catherine the Great.
Step-by-step explanation:
The country that has the Pripyat River flowing eastward as a major tributary of the Dnieper is Ukraine. This river is notably associated with the Chernobyl Disaster, as Pripyat was the city that had to be abandoned due to the nuclear power plant accident.
The Dnieper River itself has historical significance, having split territories between Russia and Poland during the 17th century and being associated with expansion under the rule of Catherine the Great.