While the regions on both sides of the river were socially and culturally interconnected, the distinct political histories of the two territories resulted in different patterns of Polish settlement there.

Catholicism was attractive among the traditionally Orthodox population due to the political late 14th century context, as the Ottoman Empire advanced into Europe.

With Constantinople encircled to a large degree after the conquest of (H)Adrianopolis, (now Edirne), in 1360, the Byzantine emperors sought a political and hopefully military ally in the Catholic west, which had crusaded against Islam to and in the Middle East before.

On 24 July 1370 the Pope instructed the archbishop of Prague and bishops of Bratislava and Kraków (Cracovia) to verify/complete the sincerity of Laţcu (although his wife remained Orthodox) and mandated them to erect such diocese covering the Moldavian state.

After Pope Gregory XI established the diocese, Polish Franciscan Andrzej Jastrzebiec was consecrated first Bishop by archbishop Florian Mokrski of Cracow.

The cathedral, dedicated to John the Baptist, was built by queen Margareth, Catholic kin of the Hungarian royal family, which in 1377 had invited Dominicans to Siret.

However prince Laţcu favoring of Catholicism met grave opposition from the Orthodox clergy, while effective Latin converts were concentrated in the north of Moldavia, near Catholic neighbour kingdoms Poland and Hungary.

[2] Even after the influence of the Ottoman Empire grew in Moldavia and the Balkans, Poles continued to be very involved in the affairs of its neighbor until the Polish Partitions end in 1795.

In 1504 the Crimean Khanate conquered the southernmost portion of Transnistria south of the Iagorlîc/Jagorlyk river along with the rest of the Yedisan region which remained under the control of the Ottoman Empire until 1792.

Thus the border between the two states was set on the Iagorlîc river, referred to as the Iahurlîc in Moldavian chronicles,[11] and in Polish source as Jahorlik or Jahorłyk[12] Because of the massive slave raids and invasions launched by the Crimean Khanate, much of the southern region of the Polish–Lithuanian Commonwealth was sparsely populated.

Polish magnates from Ukraine played a significant political and social role within the Polish–Lithuanian Commonwealth, as did the native nobility in these areas which Polonized over time.

Polish rule at this time involved the expansion of Jesuit schools and large scale construction of ornate castles and estates that included libraries, art collections, and archives that in many cases were the equal in importance to those in Poland itself.

[13] As a result of an anti-Russian insurrection in 1830, the Polish middle and poorer nobility were stripped of their legal noble status by the Russian government, and Russification policies were enacted.

[14] In spite of the ongoing migration of Poles from central Poland into Ukrainian lands,[13] by the end of the nineteenth century only three percent of the total population of these territories reported that Polish was their first language.

This trend increased in the late 1930s, as a result of the 1937-8 Polish Operation of the NKVD as well as the ceasing of educational instruction in the Moldavian ASSR for all non-Romanians populations in their native languages which was replaced by Ukrainian and Russian.

[22] The materials of the conference were published under the title Polacy w Mołdawii[23] In the period of the collapse of the Soviet Union, in 1990 professor Tadeusz Malinowski established the Polish Cultural Association (Polskie Stowarzyszenie Kulturalne) in Kishinev.