The fighting started on March 13, 1401, after the
Union of Vilnius and Radom was ratified by Polish nobles in March assuring Vytautas of Polish support. Jogaila's brother
Švitrigaila joined the war in January 1402 on the side of the Teutonic Knights as he laid claims to the throne of the Grand Duchy of Lithuania. He confirmed the Treaty of Salynas in exchange for Order's military assistance and drew Vytautas into open war against the Knights. In May 1402, Samogitians burned Memel (now
Klaipėda). Vytautas joined the fight in 1402 by attacking
Gotteswerder. The fortress surrendered after a three-day siege. In July, Švitrigaila lead the Knight's army south of Vilnius (
Medininkai,
Ashmyany,
Šalčininkai) hoping to capture the capital city. These were the last Teutonic raids into the
Lithuania proper. In April 1403, Lithuanians and Samogitians responded by raiding
Dünaburg in
Livonia. The Teutonic Knights also waged a propaganda war by sending multiple complaints to the Pope, church officials, and western rulers. They accused Vytautas of triple treachery for breaking treaties of 1384, 1390, and 1398. Vytautas responded that while Samogitia was ruled by a
military order, established to spread Christianity, Samogitians were not yet baptized.
Pope Boniface IX issued an edict prohibiting the Knights to attack Lithuania. When neither side could achieve decisive victory and Vytautas wished to concentrate his attention to troubles in
Smolensk, both sides started negotiations in summer 1403. A temporary truce was signed in December and the
Peace of Raciąż was concluded on May 22, 1404. In essence it confirmed the Treaty of Salynas. Vytautas agreed to transfer Samogitia and assist the Knight in subduing any rebellious residents. He also agreed not to accept any Samogitian families that might escape into Lithuania. In 1405 Vytautas put his words into action and helped the Knights to take control of environs of
Raseiniai,
Viduklė,
Ariogala. ==Interim peace==