Complex sentence: For some months afterwards an uneasy truce prevailed (although this did not stop Brilliana sending her men on a successful military raid into Wales against the Royalist forces), however Brilliana's health worsened and she died before the end of the year.
Split into simpler sentences: For some months afterwards an uneasy truce prevailed (although this did not stop Brilliana sending her men on a successful military raid into Wales against the Royalist forces). However Brilliana's health worsened and she died before the end of the year.