Why and how did English Parliament come into being?

1265 -In Westminster,the first English parliament conducts its first meeting in the Palace of Westminster,now also known as the "Houses of Parliament".
The Sinn Féin deputies abstained from taking their seats at Westminster and instead held the first meeting of Dáil Éireann in January 1919,where they approved the Declaration of Independence,adopted a Provisional Constitution and established a court system.British attempts to suppress what it regarded as a seditious association were met with armed nationalist resistance in what was called the War of Independence.In an effort to resolve the Irish question,Westminster passed the Government of Ireland Act,1920,which partitioned Ireland into Northern Ireland and Southern Ireland,each with its own parliament.Both parliaments would be ultimately subject to the English Parliament and would be required to send some members to sit in Westminster.The Act reorganised the court system in each jurisdiction to comprise a High Court and Court of Appeal,as well as a High Court of Appeal for Ireland to hear appeals from the respective Courts of Appeal.