From 1359 to the second half of the XVIII century Poland and Moldova had a common border. Since the XV century, most of the modern territory of Ukraine was part of the Polish-Lithuanian state. In the second half of the XVII century part of the territories bordering the Moldavian principality, was under the rule of Ukrainian hetmans. During a long historical period, Rzecz Pospolita took numerous attempts to include the Moldavian principality in its composition. Since the late 80’s of the 15 century the process of the birth of the Cossacks begins on the territory of the Polish-Lithuanian state. This process later served as the basis for the formation of the Zaporozhye Sich. The desire of the authorities of the Polish-Lithuanian Commonwealth to take control of the Zaporozhye Cossacks, to use it for their political purposes led to the activation of tripartite ethnopolitical interrelations in the territory of the Moldavian princedom during the 16th-17th centuries. This process was also furthered by the ambitions of the Cossacks themselves. The intensification of interrelationships has also affected the cultural heritage of Moldova, and its ethnic make-up, as well as the demographic situation. From the second half of the XVII century during the national liberation war, a significant part of the south-eastern territories of the Polish-Lithuanian Commonwealth was under the control of the Ukrainian hetman Bogdan Khmelnitsky. This territory was called Hetman. The upper chronological framework was defined in the 19th century. In this period the region of Bessarabia, which for the most part is part of modern Moldova, appeared after 1812 as part of the Russian Empire. As a result, for more than one hundred years, within the framework of one state, there were territories of modern Moldova, as well as parts of modern Poland and Ukraine. This circumstance could not but affect the process of the specific formation of Ukrainian identity. And in the process of ethnic history of the Moldovan population, the Ruthenian factor played a significant role.