A 1386, Grand Duke Jogaila na Lithuania ya koma Katolika kuma ya auri Sarauniya Jadwiga ta Poland.Wannan aikin ya ba shi damar zama sarkin Poland da kansa, kuma ya yi sarauta a matsayin Władysław II Jagieło har mutuwarsa a shekara ta 1434. Auren ya kafa ƙungiyar Poland da Lithuania ta sarautar daular Jagiellonian.Na farko a cikin jerin "ƙungiyoyi" na yau da kullum shine Ƙungiyar Krewo na 1385, inda aka yi shirye-shirye don auren Jogaila da Jadwiga.Haɗin gwiwar Yaren mutanen Poland da Lithuania ya kawo yankuna da yawa na Ruthenia wanda Grand Duchy na Lithuania ke iko da shi cikin tasirin Poland kuma ya zama mai fa'ida ga al'ummomin ƙasashen biyu, waɗanda suka kasance tare da haɗin gwiwa a ɗayan manyan ƙungiyoyin siyasa a Turai tsawon ƙarni huɗu masu zuwa. .Lokacin da Sarauniya Jadwiga ta rasu a shekara ta 1399, masarautar Poland ta fada hannun mijinta shi kadai.A cikin yankin Tekun Baltic, gwagwarmayar Poland tare da Teutonic Knights ya ci gaba kuma ya ƙare a yakin Grunwald (1410), babban nasara cewa Poles da Lithuanians sun kasa bibiyar wani gagarumin yajin aiki a kan babban wurin zama na Teutonic Order a. Malbork Castle.Ƙungiyar Horodło na 1413 ta ƙara bayyana dangantakar da ke tsakanin Masarautar Poland da Grand Duchy na Lithuania.