In a decentralised system such as public international law with its many specialised subfields, the question of how to conceptualize the relationship and interplay of its distinct subfields becomes especially salient. Moreover, this question becomes even more acute when these subfields simultaneously claim authority and possibly arrive at quite different, if not conflicting, results. In the case of civil war, a foreign investor’s production site may be destroyed. This may lead to a breach of a bilateral investment treaty if government forces are deemed sufficiently responsible for such a destruction. However, in remarkable contrast to this, under international humanitarian law of non-international armed conflicts, if the destruction was justified under the principle of ‘military necessity’, then this state action could be considered lawful. If a conflict between the norms of both regimes arises here at all, should it be resolved by the principle of lex specialis? Or should rather a more informative approach be taken? Shall therefore the extended war clause contained in bilateral investment treaties—which offers compensation for investments demonstrably destroyed in cases in which the destruction was not required by the ‘necessity of the situation’—be interpreted in the light of humanitarian law’s principle of military necessity? Or, are there compelling arguments for an autonomous treaty interpretation on its own terms? Finally, the question is raised whether the burden of proof remaining on the plaintiff investor in these specific constellations is compatible with the principle of procedural equality.