Complex sentence: However, Bosniak and Croat politicians began the process of attempting to suspend the referendum with the support of the High Representative for Bosnia and Herzegovina and the Constitutional Court of Bosnia and Herzegovina, claiming it was a violation of the Dayton Agreement.
Split into simpler sentences: However, Bosniak and Bosnian Croat politicians began the process of attempting to suspend the referendum. The High Representative for Bosnia and Herzegovina and the Constitutional Court of Bosnia and Herzegovina claimed that the vote would have constituted a violation of the Dayton Agreement.