Nobles in this country were granted equality after the passage of the Golden Liberty. A ruler of this country known as "the Brave" was the first to unite it, and was a member of the Piast dynasty. Members of this country's nobility also sat in its legislature, in which all members had a veto power that nullified the laws passed in any given session. That legislature was called the Sejm ["same"]. After the signing of the Union of Lublin, this nation formed a commonwealth with Lithuania. A king of this nation relieved a siege at Vienna, turning back an Ottoman invasion of Europe. For 10 points, 
Nobles in this country were granted equality after the passage of the Golden Liberty. A ruler of this country known as "the Brave" was the first to unite it, and was a member of the Piast dynasty. Members of this country's nobility also sat in its legislature, in which all members had a veto power that nullified the laws passed in any given session. That legislature was called the Sejm ["same"]. After the signing of the Union of Lublin, this nation formed a commonwealth with Lithuania. A king of this nation relieved a siege at Vienna, turning back an Ottoman invasion of Europe. For 10 points, name this nation which was ruled by men like Jan III Sobieski from Warsaw.