Two Concepts of Non-Recognition
International humanitarian law is not equipped to define the legal consequences of systematic ultra vires acts of an occupying power. A more satisfactory conception of non-recognition demands either an evolution in the law of occupation or an untethering from it.
In the context of occupation, the term 'non-recognition' is used to describe two discrete concepts, one broad and one narrow, which are often conflated. The broad conception postulates that because the authority of an occupying power is severely circumscribed relative to that of a sovereign, to preserve the rights of the lawful sovereign, third parties must not recognize or give effect to acts that exceed that authority. The narrow conception is that codified in Article 41(2) of the ILC Articles on State Responsibility: the duty of states not to recognize as lawful, nor render aid or assistance in maintaining, a situation created by a serious breach of a preemptory norm of international law.
Neither conception is satisfactory, in theory or in practice. The broad conception is too broad: not every ultra vires act of an occupying power can or should trigger international obligations. The narrow concept is too narrow: international obligations should not be limited to serious breaches of a handful of recognized preemptory norms.
The inadequacy of both conceptions is attributable to the limitations of IHL in defining the legal consequences of systemic ultra vires acts.  The law of occupation is (for good reason) agnostic on the legality of the use of force resulting in the occupation. It applies as long as the occupying power retains effective control, irrespective of demographic or legal changes made by the occupying power in respect of the occupied territory. In terms of the protection of civilians, IHL’s virtue is that an occupying power cannot ‘shake it off’ through even the most blatant or systematic violations. But this same trait is a liability when it comes to vindicating fundamental norms of the international order perverted through occupation – the self-determination of peoples and the sovereign equality of states.
Although IHL defines the legal consequences of grave breaches (erga omnes effect), it does not define the consequences of the systemic or persistent commission of such violations. While the settlement of the occupying power’s nationals in occupied territory is a grave breach giving rise to an erga omnes duty to cooperate towards its suppression, IHL does not define the legal consequences arising once a sustained practice of establishing settlements ultimately destroys, in demographic rather than legal terms, the separate and distinct status of the occupied territory, and with it the prospect of restoring (at least external) self-determination.
Thus, IHL is not equipped to define the legal consequences of systematic ultra vires acts of the occupying power. Such acts may have enduring or even permanent consequences for the self-determination of the people of the occupied territory. As such, they would seem to implicate a recognized preemptory norm. Yet preemptory norms are defined in the first instance by their legal consequences, consequences IHL do not provide.  A more satisfactory conception of non-recognition thus demands either an evolution in the law of occupation or an untethering from it.
 The literature on IHL's inadequacy to address prolonged and transformative occupations, and by extension conquest under the guise of occupation, is growing and includes, e.g., ICRC, Expert Meeting: Occupation and Other Forms of Administration of Foreign Territory (2012); Orna Ben-Naftali et al., “Illegal Occupation: Framing the Occupied Palestinian Territory,” 23 Berkeley J. Int’l L. 551 (2005); Aeyal Gross, The Writing on the Wall: Rethinking the International Law of Occupation (2017).
 See Georges Abi Saab, The Uses of Article 19, 10 Euro J. Int’l L. 339, 349 (1999) (advocating for the ultimately-abandoned draft Article 19 of the Articles of State Responsibility, which would have recognized “crimes of state” (as opposed to ordinary “international delicts”) defined substantively rather than by their legal effects, on the basis that to “define jus cogens in the context of state responsibility in this substantive manner … would resolve the problem of tracing the ambit of the aggravated or triangular regime of responsibility.”)