Coolsaet has also written extensively on international relations, mostly in Dutch. Between 2005 and 2016, his "Macht en Waarden in de Wereldpolitiek" ("Power and Values in World Politics", Academia Press) provided for a yearly overview of major trends in global politics. A 2008 publication, "De geschiedenis van de wereld van morgen" ("A History of Tomorrow’s World", Van Halewyck), analyzed long-term change patterns in international relations. Upon publication in February 2008, this book appeared on the Belgian bookshops' bestseller list for several months.