The expansion of the Russian's Empire to south-west was part of the Tsars imperial policy since the time of Peter I, also known as Peter the Great.
In parallel with the conquest of the Baltic Sea an access should be created to the Black Sea, the straits and the Balkans. In the 18th century in a series of wars Russian armies conquered large parts of the steppe regions in the north and east of the Black Sea which until then were under the influence of the khanate of the Crimean Tatars.
The taking of possession of this land has created many problems. If on the one hand the serfdom unabled the colonization of new land with farmers, on the other hand constant incursions of nomadic people created many hardships.
Till 1774 Russia was able to break the supremacy of the Ottomans in the north coast of the Black Sea and could make sure the navigation in the Black Sea and the straits.
The Russian war strategy was not only concerned to territorial expansion or economic development, but considered himself also as a protective power of the Orthodox Christians who were still under Ottoman's rule. So it felt legitimized to act in support of the Christian subjects of the Sultan in the Balkans and the right in military occupation of Moldavia and Wallachia.
Both Danube principalities were repeatedly warlike scenarios in the Russian-Ottomans wars1. They had a key geopolitical position in the Russian Oriental and Balkan policy, as were the gateway to the Russian army in South-East. From here Russia could strengthen its influence in the Balkans and give greater emphasis to drive out the Ottomans from Europe.
1 Russian-Turkish wars or Russian-Ottoman wars were a succession of 11 wars between the Russian Empire and the Ottoman Empire. Between the individual battles were an average of 13 years. In their course, the Ottoman Empire had to gave up gradually areas around the Black Sea to Russia. The war efforts and defeats brought the Ottoman Empire to interior ruin e decline.