 Complete the following phrase:  On 31 May 1380, Jogaila and Grand Master Winrich von Kniprode signed the secret Treaty of Dovydiškės. Based on the terms of the accord, Jogaila agreed not to intervene during attacks by the Teutonic Knights against Kęstutis or his children. However, if providing aid to Kęstutis would be necessary to help to avoid any suspicions, it would not be a violation of the treaty. It remains controversial as motives behind the treaty are not entirely clear. Some historians blamed Uliana, mother of Jogaila, or his adviser Vaidila, while others pointed out generational differences: Kęstutis was about 80 years old and determined not to accept Christianity while Jogaila was about 30 years old and was looking for ways to convert and modernize the country. Still others suggested that the treaty was primarily directed against Andrei and his allies  brother Dmitry of Bryansk and Grand Duke of Moscow Dmitri Donskoi. Jogaila, having secured his western front, allied himself with the Golden Horde against the Grand Duchy of Moscow for the upcoming 