Chicken War or Hen War (Polish: Wojna kokosza) is the colloquial name for a 1537 anti-royalist and anti-absolutist rokosz (rebellion) by the Polish nobility.
The derisive name was coined by the magnates, who for the most part supported the King and claimed that the conflict's only effect was the near-extinction of the local chickens, which were eaten by the nobles gathered for the rokosz at Lwów, in Ruthenian Voivodeship.
Bona Sforza (2 February 1494 – 19 November 1557) was Queen of Poland and Grand Duchess of Lithuania as the second wife of Sigismund the Old, and Duchess of Bari and Rossano by her own right. She was a surviving member of the powerful House of Sforza, which had ruled the Duchy of Milan since 1450.
Smart, energetic and ambitious, Bona became heavily involved in the political and cultural life of the Polish–Lithuanian union. To increase state revenue during the Chicken War, she implemented various economic and agricultural reforms, including the far-reaching Wallach Reform in the Grand Duchy of Lithuania. In foreign policy, she allied with the Ottoman Empire and sometimes opposed the Habsburgs. Her descendants became beneficiaries of the Neapolitan sums, a loan to Philip II of Spain that was never completely paid.