Both Peter the Great and Catherine the Great were rulers that, during their reigns, aimed at modernized Russia and at expanding its borders; and since Russia was a landlocked nation, both rulers aimed to gain a warm-water port on the Black Sea. With a warm-water port, Russia would have a port that was available all year-round, which was necessary for Russian commerce and sea-communications in Europe.
Under this task, Peter the Great fought the Ottoman Empire in order to gain the warm-water port and other territories but he was defeated. Several years later, Catherine succeeded to gain the warm-water port on the Black Sea and expand Russia's borders even more in one of the many Russo-Turkish wars.