However, over time it became clear that closer economic and monetary co-operation was desirable for the internal market to develop and flourish further, and in 1991 the Member States approved the Treaty on European Union (the Maastricht Treaty), deciding that Europe would have a strong and stable single currency for the 21st century.
Le himeacht ama, áfach, ba léir gurbh fhearr comhoibriú eacnamaíoch agus airgeadaíochta níos dlúithe ionas go bhforbrófaí agus go dtiocfadh borradh sa bhreis faoin margadh inmheánach agus sa bhliain 1991 d’fhaomh na Ballstáit an Conradh ar an Aontas Eorpach (Conradh Maastricht), a chinntigh go mbeadh airgeadra aonair a bheadh láidir agus cobhsaí ag an Eoraip sa 21ú haois.