more difficult to prove why it did not act. For this reason, the necessity of demonstrating that a behavior was prompted by a sense of legal obligation makes it particularly difficult for customary international law to develop around the prohibition of a practice. One important case in the development of modern customary international law theory is the Lotus case, in which France attempted to protest Turkey's assertion of criminal jurisdiction over a French citizen for acts committed on the high seas (outside of Turkey's territory). France presented a number of historical examples to demonstrate that the state of nationality or the state whose flag the ship had flown had exclusive jurisdiction in cases such as this. However, the Permanent Court of International Justice (a precursor to the ICJ) declared that the evidence showed merely that "States had often, in practice, abstained from instituting criminal proceedings, and not that they recognized themselves as being obliged to do so; for only if such abstention were based on their being conscious of having a duty to abstain would it be possible to speak of an international custom." This reasoning was cited approvingly in the North Sea Continental Shelf cases, which similarly declined to find the existence of customary law regarding the proper method to delimit territorial claims to the continental shelf extending from the coastline of states bordering the North Sea. The ICJ also declined to find evidence of customary international law in an opinion on the legality of the use or threat of nuclear weapons, despite what some argued to be uniform state practice. As in the North Sea Continental Shelf cases, in the advisory opinion on the Legality of the Threat or Use of Nuclear Weapons it found that the mere fact that no state had used nuclear weapons against another state since World War II did not reflect opinio juris. Some states had pointed out that a series of U.N. resolutions had been issued "that deal with nuclear weapons and that affirm, with consistent regularity, the illegality of nuclear weapons," and argued that this signified “the existence of a rule of international customary law which prohibits recourse to those weapons.” Nonetheless, the ICJ wrote that states possessing nuclear weapons had almost always objected to these resolutions, which strongly suggests that those states did not believe that a customary law prohibiting their use existed. Moreover, it wrote that the non-use of