Reflections in View of Spanish Practice
It may be said that the main cause of the fragmentation of international investment law is the specific drafting of the treaties that regulate this topic, particularly bilateral investment treaties between States (“BITs”).
Two factors should be taken into account in this regard:
On the one hand, an international treaty only binds States party thereto (res inter alios acta) and has effect, in principle, on neither non-signatory third-party States (pacta tertiis nec nocent nec prosunt) nor, by extension, nationals of those third-party States.
On the other hand, according to the most recent UNCTAD estimates, 182 States and territories are parties to at least one BIT, with 3,240 international investment agreements (“IIAs”) having been signed as of 2013. In addition, most of these treaties respond to the same structure with substantive and procedural protections for foreign investments, notwithstanding some differences among them (sometimes particularly relevant). It is therefore reasonable to suggest that, despite the res inter alios acta principle, an IIA should not be considered in complete isolation, but rather as a piece of a system which, by definition, should be linked with the rest of elements of that system.
New Trends in International Economic Law. From Relativism to Cooperation, 2018.