Complex sentence: When Schuman's first government had proposed the creation of a European Assembly, it made the issue a governmental matter for Europe, not merely an academic discussion or the subject of private conferences, like The Hague Conference of the European Movements earlier that year.
Split into simpler sentences: When Schuman's first government had proposed the creation of a European Assembly, it made the issue a governmental matter for Europe. It became more than an academic discussion or the subject of private conferences, like The Hague Conference earlier that year.