[1] Registered Cossacks became a military formation of the Commonwealth army beginning in 1572[2] soon after the Union of Lublin (1569), when most of the territory of modern Ukraine passed to the Crown of Poland.

The first recorded official plan for enlisting Cossack formations as a border service in Poland-Lithuania was brought to the State Council of the Grand Duchy of Lithuania in 1524 by Semen Polozovic and Kristof Kmitic.

With the start of the Livonian War of 1558–1583, the voivode of Kiev, Konstanty Wasyl Ostrogski, and the starosta of Cherkasy, Alexander Wiśniowecki, recruited Cossacks into their armies, while in 1568 King and Grand Duke Sigismund II Augustus sent a proposition to the Zaporizhian Sich to join his foreign campaign and to sign up for royal service.

Sigismund II Augustus decreed the formation of registered Cossacks on June 5, 1572[2] when the King confirmed the orders of Great Crown Hetman Jerzy Jazłowiecki, the voivode of Podole and Ruthenia, for state service.

Batory also ordered the voivode of Kiev, Konstanty Wasyl Ostrogski, to send a punitive expedition against Pidkova and asked the mayors of Khmilnyk, Bar, Bratslav, Vinnytsia, Bila Tserkva and others to support him.

The Cossacks frequently and proudly pledged their allegiance to serve the King of Poland and hoped for at least the same financial compensation as the regular army.

A royal edict issued on July 25, 1590, envisaged registering 1,000 Cossacks for policing duty in order to prevent unauthorized raids into neighboring countries.

A substantial minority of Cossacks formed skilled light cavalry units (choragiew), excellent skirmishers trained in mounted archery (and later using firearms), making lightning raids, harassing heavier, slower formations and disengaging.

Registered Cossacks had many privileges, including personal freedom, exemption from many taxes and duties, and the right to receive wages, although the Commonwealth military's fiscal problems, led to delayed payments, often via items like clothing or weapons instead of coin.

Many Cossacks were skilled warriors and their major income source came from raids on the southern neighbors of the Commonwealth: the (Ottoman Empire and its vassals).