On 1 July 1569, Polish and Lithuanian nobles signed "The Union of Lublin". This momentous event was the result of several years of contentious negotiations in the Sejm, i.e. Parliament. The loose union by marriage of the Kingdom of Poland and Grand Duchy of Lithuania was about to end since the last member of the Jagiellonian Dynasty, Sigismund II Augustus, was childless after three marriages.
The immediate result was a federated state - the Polish-Lithuanian Commonwealth - which at once was one of the largest and most populous in Europe and an elected king - King Henryk Walezy. It also resulted in the ceding of Podhalia, Volhynia, Podolia, and Kiev to the Polish Crown by Lithuania and the loss of autonomy by Royal Prussia.
However, there were many unresolved issues which needed to be addressed. These unresolved issues were decided four years later with the signing of "The Golden Liberty" in 1573.
And nearly all of these peaceful advancements in government and social thinking were made possible through the lucrative agricultural export market known as "The Grain Trade".