Complex sentence: Here the majority of the Hanse members decided in a Hanseatic diet on 1 May 1388 for an embargo against the Flemish cities, while Prussia could not prevail with its plea for further negotiations.
Split into simpler sentences: Here the majority of the Hanse members decided in the Hanseatic Diet on 1 May 1388 for an embargo against the Flemish cities. Meanwhile Prussia could not prevail with its plea for further negotiations.