In 1389, Vytautas started a civil war against Skirgaila, Jogaila's unpopular regent in Lithuania. Skirgaila was appointed after Jogaila signed the Union of Krewo in 1385 and was crowned King of Poland in 1386. The Lithuanians were dissatisfied with the growing Polish influence in Lithuania. Vytautas promised Samogitia to the Teutonic Knights in reward for their military assistance. Their joint armies made frequent incursions into Lithuania; the largest attack was launched in the early fall of 1390 when Vilnius was besieged for five weeks. Invaders managed to capture the Crooked Castle and turn much of the suburbs into ruins, but failed to take the city. Both sides realized that a quick victory would be impossible and raids were devastating the same country which they sought to rule. Polish nobles were dissatisfied that Jogaila spent so much attention on Lithuanian matters and that the Union of Krewo did not bring the expected results. In such situation Jogaila decided to seek a compromise with Vytautas.