The end of the 16th century was marked by a final phase of rivalry between the remaining Catholics and the new Protestant communities. In 1592, Gustav Vasa's Catholic grandson and king of Poland, Sigismund, ascended the Swedish throne. He pursued to strengthen Rome's influence by initiating Counter-Reformation and created a dual monarchy, which temporarily became known as the Polish-Swedish Union. His despotic rule, strongly characterized by intolerance towards the Protestants, sparked a civil war that plunged Sweden into poverty. In opposition, Sigismund's uncle and successor, Charles Vasa, summoned the Uppsala Synod in 1593 which officially confirmed the modern Church of Sweden as Lutheran. Following his deposition in 1599, Sigismund attempted to reclaim the throne at every expense and hostilities between Poland and Sweden continued for the next one hundred years.