UNION OF WILNO

The 'Wilno Pact' was an agreement reached on November 28, 1561 between Sigismund II Augustus and the Livonian Brothers of the Sword. The order was secularized, Courland and Semigalia became the Duchy of Courland and were granted to Gotthard Kettler. Grand Duchy of Lithuania gained Riga and the rest of Livonia, though these lands regained some autonomy.
The Pact resulted in the Northern Seven Years' War.