Benjamin wrote: I don't know much about the Formosa province or if it is still disputed by Paraguay, but the UN does not consider that territory a colony either.
You may wish to read up on this.
After the Paraguayan War ended in 1870 the Argentine government proposed to Brazil that Paraguay be partitioned between them and permanently abolished as a country. Paraguay only survived because Brazil wouldn't agree to the Argentine proposal, preferring instead to use the rump Paraguayan state as a buffer between it and Argentina, realising the potential dangers of future rivalry between the two countries if there was a long common border between them. They also objected to Argentine annexation of Encanacion for the same reason.
Formosa was of more strategic rather than economic significance, with the control of river space and having Asuncion within easy reach if Paraguay were to become a problem.
In the last thirty years or so Formosa has had quite a lot of money invested in it by Argentine governments and I believe is now one of the fastest growing economically of Argentina's provinces. Paraguay has made no inclination to recover its lost teritories, which includes part of Corrientes as well as Formosa (to Argentina) and the Matto Grosso territories annexed by Brazil. But then Paraguay is in no position to demand them back - not least because it would imply also returning territory to Bolivia taken as a result of the Chaco War.
''Give me a Ping and one Ping only'' - Sean Connery.