Why is the EU the leading trading partner with Mercosur and not the U.S.?

Question

Why is the EU the leading trading partner with Mercosur and not the U.S.?

Answer 1

Because the Us is a terrible buisiness partner..anyone who does trading with the US ends up loosing!

Answer 2

The Mercosur was created by Argentina, Brazil, Paraguay and Uruguay in March 1991 with the signing of the Treaty of Asuncion, in much the same way that the European Union was created in 1992 with the signing of the Treaty on European Union.  

The EU (and its predecessor, the European Commission) have supported Mercosur from the beginning, no doubt in part because of of their parallel paths - both unions were originally set up with the synergistic goal of creating a common market/customs union between the participating countries on the basis of various forms of economic co-operation.

The US has not been so involved.