Dealing with similar enemies, the countries of Poland and Lithuania were joined in the dynastic Union of Krewo. This alliance allows Poland to draw upon the lithuanian noblemen, the Bajorai.
Available to: Poland
Researched at: Town Hall
Effect: enables Bajoras
The Kingdom of Poland was united with the Grand Duchy of Lithuania in something of a surprise move, when the 'King' Jadwiga cancelled her engagement with Sigismund of Luxembourg, who would later become Emperor, and married Grand Duke Jogaila in stead, who ascended the Polish throne as Wladyslaw II. Jagiello.
This event prevented the personal union of the Holy Roman Empire and Poland and no doubt contributed to the country's lasting political independence. The Union of Krewo, personal union between the Kingdom of Poland and the Great Principality of Lithuania of 1385 in the Castle of Krewo, strengthened Poland's military with the addition of the skilled Lithuanian nobility. These were more lightly armed than their Polish equivalents and had in part copied their tactics from the Mongols.
The Polish nobility was already dissatisfied with the dynastical connection to Hungary, but shared common interestes with Lithuania against the Teutonic Order. Together, the two countries fought against the Order and inflicted a very major defeat on it in 1410 at Grunwald or Tannenberg.