Complex sentence: In Stockholm on 4 November 2009 an Arbitration Agreement between Croatia and Slovenia was finally signed by the EU President and both countries' prime ministers, and a subsequent referendum in Slovenia authorized the use of binding arbitration.
Split into simpler sentences: In Stockholm on 4 November 2009, an Arbitration Agreement between Croatia and Slovenia was finally signed by both countries' prime ministers as well as the EU President. A subsequent referendum in Slovenia authorized the use of binding arbitration.