In this paper, I highlight that international investment law, as a subsystem, should evolve to accept rules from other subsystems of law, e.g., human rights, trade (WTO law and RTA law), and environmental. This proposed evolution would need to include the acceptance of new tools that would help to expand the traditional sources of international law when dealing with fragmentation problems. Those tools would be used as connecting rules (Drive-Chains) among the fragmented subsystems when reviewing justifications not provided in investment treaties, giving coherence, predictability and legitimacy to the investment subsystem with others subsystems of law.