Hello,

accordding to the wikipedia:
https://en.wikipedia.org/wiki/Novgorod_Republic

In 1389 the newly appointed Prince of Novgorod, Lithuanian prince Lengvenis, paid homage from the Novgorod territories to Polish King Władysław II Jagiełło in Sandomierz, thus the Novgorod Republic became a fiefdom of the Kingdom of Poland.[14] Novgorod troops under the command of Lengvenis took part in the Battle of Grunwald (1410) on the Polish–Lithuanian side.


How about making Novgorod a vassal of Poland after 1389?