Here's a short story:

The szlachta ([ˈʂlaxta] ( listen), exonym: Nobility) was a legally privileged noble class with origins in the Kingdom of Poland. It gained considerable institutional privileges between 1333 and 1370 during the reign of King Casimir III the Great.:211 In 1413, following a series of tentative personal unions between the Grand Duchy of Lithuania and the Crown Kingdom of Poland, the existing Lithuanian nobility formally joined this class.:211 As the Polish-Lithuanian Commonwealth (1569–1795) evolved and expanded in territory, its membership grew to include the leaders of Ducal Prussia, Podolian and Ruthenian lands. 

The origins of the szlachta are shrouded in obscurity and mystery and have been the subject of a variety of theories.:207 Traditionally, its members were owners of landed property, often in the form of "manor farms" or so-called folwarks. The nobility negotiated substantial and increasing political and legal privileges for itself throughout its entire history until the decline of the Polish Commonwealth in the late 18th century. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: Where are they from?
Guess: Poland

Question: They were in power until?
Guess: late 18th century

Question: Who qualified to be part of this group?
Guess: noble class

Question: What did they need to possess?
Guess: landed property

Question: Under whom did they gain power?
Guess: King Casimir III the Great

Question: Who else was added later?
Guess: the existing Lithuanian nobility

Question: When?
Guess: 1413

Now answer the following question in the same format.

Question: Where did it expand?

Ducal Prussia, Podolian and Ruthenian lands.