[1] His reigns were concurrent with the period of Romanian and Eastern European history known as the Moldavian Magnate Wars, a long conflict in the early modern states of Moldavia, Wallachia, and Transylvania, in which the Moldavian state was alternatively influenced by the Austrian Habsburgs, the Ottoman Empire, and the Polish–Lithuanian Commonwealth.

Stefan's relations with the Commonwealth, however, were less than cordial, and his first reign would be beset by conflict with the Polish aligned members of Moldavia's nobility and the powerful Movila family.

In addition to taking part in battles with the Polish and the Movilești, Stefan Tomsa IX was also known for his extensive building projects, including a large monastery in the village of Solca, and for attempting to improve the lives of the poor in curbing the power of the major boyars.

In 1612, the Movilas and their allies, which included influential Moldavian boyars and statesmen Nicoară Prăjescu, Stroici, Dumitru Buhuș, and Pătrașcu Ciogolea pleaded for support from Poland.

Tomsa raised an army which included mercenaries, Ottomans, and a sizable detachment of Crimean Tartars under his ally, the powerful Khan Temir (or Cantemir) Bey to meet them.

Stefan Tomsa's forces were victorious, and relations between the Turks and the Poles continues to deteriorate which culminated in the Polish–Ottoman War (1620–1621).