Complex sentence: On 15 January 2015, after Islamic State's conquests in Libya, Renzi conducted a long phone call with Sisi, to discuss the terrorist threat in the Mediterranean; the two leaders agreed that the next steps should be political and diplomatic efforts through the United Nations.
Split into simpler sentences: On 15 January 2015, after Islamic State's conquests in Libya, Renzi conducted a long phone call with Sisi, to discuss the terrorist threat in the Mediterranean. The two leaders agreed that the next steps should be political and diplomatic efforts through the United Nations.