Short answers, pulled from the story.
The early Vasa era began with the reconquest of Stockholm by Gustav Vasa in June 1523, following the Stockholm Bloodbath of 1520 in which Christian II of Denmark seized the city. Gustav Eriksson gathered troops from Dalarna and support from Lübeck, was elected monarch by his men in August 1521, and completed the Swedish War of Liberation by June 1523. Sweden's secession from the Kalmar Union followed.
Eric XIV was dethroned in 1568 following a magnates' uprising led by his brother John. His reign was destabilized by periods of insanity beginning in 1567, which contributed to the Sture Murders that year and the imprisonment of John. A coalition of nobles and John himself forced his removal.
The Uppsala Synod of 1593 was a church assembly summoned by Duke Charles after the death of John III. On the 5th of March 1593, it rejected John's Catholic-leaning liturgy, declared Holy Scripture and the three primitive creeds as the foundations of Christian faith, and adopted the Augsburg confession. It finalized Sweden's Lutheran doctrines and directly triggered Sigismund's return and the civil war that ended his reign.
John III persuaded a synod in Stockholm in 1574 to adopt articles he had written himself, issued a new church ordinance in February 1575 approximating the patristic church, and in 1576 introduced a new liturgy modeled on the Roman missal. He also sent an embassy to Rome to negotiate reunion with the Holy See and received the Jesuit Antonio Possevino in Stockholm. John ultimately declined to convert because Rome would not meet his conditions.
Sigismund was elected king of Poland on the 19th of August 1587. Sixteen days later, the Articles of Kalmar, signed by his father John III and Sigismund, set the terms: the two kingdoms would be in perpetual alliance but each would keep its own laws, Sweden would retain its Lutheran religion, and no new taxes would be levied in Sweden during Sigismund's absence. Sweden was never to be administered from Poland.
At the Battle of Stangebro on the 25th of September 1598, Duke Charles and the Protestant faction defeated Sigismund, deciding the civil war that had become inevitable after the Uppsala Synod. Sigismund fled Sweden and never returned. On the 19th of March 1600, the Riksdag of Linkoping formally proclaimed Duke Charles king under the title of Charles IX of Sweden.