Final answer:
The Dnieper River is the one that flows through Kiev and Dnipro. It has historically been significant, marking territorial divisions and facilitating trade due to its strategic location.
Step-by-step explanation:
The river that flows through Kiev and Dnipro (formerly called Dnipropetrovsk) is the Dnieper River. This river has had significant historical importance as it served as a demarcation line during the 17th century, where Russian and Polish territories in what is now Ukraine were divided along its course.
The capital of Kievan Rus', which was a powerful confederation of city-states in the 9th century, was Kiev, situated on the Dnieper. This location was strategic for the trade routes linking the Black Sea and the Baltic Sea. The Dnieper River's fertile riverlands have been of interest to various empires throughout history, including that of Catherine the Great who sought to expand the Russian Empire.