Nevertheless, subsequent attempts on the part of Poland to subordinate Lithuania drove Witowt for the third time into the arms of the Order, and by the treaty of Salin in 1398, Witowt, who now styled himself Supremus Dux Lithuaniae, even went so far as to cede his ancestral province of Samogitia to the knights, and to form an alliance with them for the conquest and partition of Pskov and Great Novgorod.
The result was a whole series of wars with the Teutonic Order, which now acknowledged Swidrygiello, another brother of Jagiello, as grand-duke of Lithuania; and though Swidrygiello was defeated and driven out by Witowt, the Order retained possession of Samogitia, and their barbarous methods of "converting" the wretched inhabitants finally induced Witowt to rescue his fellow-countrymen at any cost from the tender mercies of the knights.
Olgierd was succeeded by his son Jagiello as grand duke in 1377, while Kiejstut was left in possession of Samogitia, Troki and Grodno; but the Teutonic Order, alarmed at the growth of Lithuania, succeeded in estranging uncle and nephew, and Kiejstut was treacherously assassinated by Jagiello's orders, at Krewo, on the 15th of August 1382.
Three weeks later Jagiello was compelled to cede Samogitia, as far as the Dubissa, to the Knights, and, in the following year they set up against him Kiejstut's son Witowt.
Skilfully taking advantage of the jealousies of Poland and Lithuania, as they were accentuated by the personal antagonism of Jagiello and Witowt (q.v.), with the latter of whom the Knights more than once contracted profitable alliances, they even contrived (Treaty of Salin, 1378) to extend their territory by getting possession of the province of Samogitia, the original seat of the Lithuanians, where paganism still persisted, and where their inhuman cruelties finally excited the horror and indignation of Christian Europe.