Bha e na neach leantainn do [[Richard II]], rìgh Shasainn. Ach nuair a chaill Richard a' chumhachd aige chaidh cuid dhen fhearainn a bha aig Glyndŵr a thoirt air falbh le Reginald Grey, 3mh Baran Grey de Ruthyn, <ref name=bbchistory/> neach-leantainn Henry IV a bha a' fàs na bu treasa aig an àm ud.
Glyndŵr sought help from Henry IV to deal with his land being taken, but Henry refused to take action against his supporters. Glyndŵr also failed to supply soldiers to the king for another attack on Scotland. Grey called him a traitor. Glyndŵr decided to take action against Henry IV. He gave himself the title of Prince of Wales in September 1400, and began a series of attacks against Grey and towns along the borders with England. Henry IV sent his army to Wales to fight Glyndŵr and regain control, but it had the opposite effect. It became a widespread rebellion against England.<ref name=bbchistory/>
In April 1401 Glyndŵr's army captured [[Conwy Castle]].<ref name=bbchistory/> The next year, at the [[Battle of Bryn Glas]], also known as the Battle of Pillethl, Glyndŵr defeated the English army, and captured its leader, [[Edmund Mortimer]].<ref name=bbchistory/> By 1404 a French army had landed, and together with the Welsh army they attacked [[Worcester]].<ref name=bbchistory/>