Vytautas began his reign as the Grand Duke. It is not entirely known what powers were given to him by Jogaila, but he had considerable independence. He replaced some of Jogaila's brothers and supporters with trusted viceroys appointed from Lithuanian nobles: Skirgaila was removed from Polotsk, Švitrigaila from Vitebsk, Kaributas from Severian Novgorod, Vladimir from Kiev, Fyodor Koriatovych from Podolia, and Fyodor Lubartovich from Volhynia. He also made territorial secession in 1398 without approval from Jogaila. While Skirgaila always signed documents first in the name of Jogaila and only then in his own name, Vytautas used only his own name. Lithuania was drifting away from Poland, but the defeat of Vytautas army in the Battle of the Vorskla River against the Golden Horde in 1399 forced to renew the union and conclude the Union of Vilnius and Radom in 1401. It legalized Vytautas independence in the Grand Duchy giving him all the powers of sovereign ruler. However, after his death all lands and powers were to return to the King of Poland. The two countries turned their joint forces against the Teutonic Knights delivering a crushing defeat in the Battle of Grunwald in 1410.