poland and lithuania underwent an alternating series of wars and alliances during the 14th century and early 15th century. several agreements between the two (the union of kraków and vilna, the union of krewo, the union of wilno and radom, the union of grodno, and the union of horodło) were struck before the permanent 1569 union of lublin. this agreement was one of the signal achievements of sigismund ii augustus, last monarch of the jagiellon dynasty. sigismund believed he could preserve his dynasty by adopting elective monarchy. his death in 1572 was followed by a three-year interregnum during which adjustments were made to the constitutional system; these adjustments significantly increased the power of the polish nobility and established a truly elective monarchy.