August 9 In Swedish History

A Vasa descendant is elected to the throne in Poland. 

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  August 9, 1587—Sigismund Vasa is chosen as King of Poland, the coronation followed on December 27 the same year.

• August 9 In Swedish History
  1587: Sigismund Vasa is chosen King of Poland. Born June 20 in 1566, Sigismund III Vasa was the son of King Johan III of Sweden and his first wife, Katarina Jagellonica of Poland. Elected to the throne of the Polish–Lithuanian Commonwealth, Sigismund sought to create a personal union between the Commonwealth and Sweden (Polish–Swedish union), and succeeded for a time in 1592.
  After he had been deposed in 1599 from the Swedish throne by his uncle, Karl IX, and a meeting of the Riksens ständer (Swedish Riksdag), he spent much of the rest of his life attempting to reclaim it. Sigismund remains a highly controversial figure in Poland. His long reign coincided with the apex of the Polish–Lithuanian Commonwealth's prestige, power and economic influence. On the other hand, it was during his reign that the symptoms of decline leading to the Commonwealth's eventual demise surfaced. Popular histories tend to present Sigismund as the principal source of these destructive processes; whereas academic histories are usually not damning of him. However, the question of whether the Commonwealth's decline was caused by Sigismund's decisions or had its roots in historical processes beyond his personal control, remains a highly debated topic. Sigismund died in 1632.
  His two sons were to become the last of the Vasa dynasty: Vladislav IV, King of Poland, grand dutch of Lithuania, 1632–1648, but never king of Sweden, succeeded by his younger brother, Johan II Kasimir (1648–1668)