force in their own circumstances. They place more faith in future leaders, commanders, and judges to come to better conclusions in reviewing the use of force after the fact than in the prescience of today’s treatymakers. An approach built on flexible standards allows nations to gather more knowledge about the effects of new weapons, under conditions of deep uncertainty, before reaching fundamental decisions of policy.
In this respect, customary rules on the use of force resemble a common-law standard, such as the classic legal norm of reasonableness. A standard such as reasonableness allows judges to consider the totality of the circumstances before ruling on whether a defendant’s actions were legal. A strict rule, however, such as contributory negligence, imposes a clear norm that reduces liability to a single factor and precludes the influence of later circumstances. Rules reduce decision costs because they are clear and easy to apply, they create legal certainty and predictability, and they require less gathering of information. Rules, however, prevent a nuanced application of law to facts and so often result in inequitable outcomes. Standards demand higher decision costs because of the need for more information and time for consideration. Standards produce greater uncertainty and unpredictability, but they more often produce the better answer. A rule gives more power to the legislators who write the norm earlier and narrow the discretion of future officials, while a standard places more trust in the competence and knowledge of later decisionmakers.19 By following custom, the law of war accepts that the lawfulness of the use of force depends far more on the circumstances, that later officials will have greater access to information and experience, and that it is more important to get right answers than fast answers.
Many international leaders and scholars would replace the millennial-old, customary approach to the rules of war with instant law—with strict rules rather than standards. Nations launched an ambitious movement to codify new rules of military operations in 1977 with Additional Protocol I to the Geneva Conventions (AP I).20 Controversially, AP I promoted two significant changes to the laws of war. First, it elevated non-state actors, such as independence movements and guerrillas, to the same status as nations with conventional armed forces. Second, it attempted to reduce the discretion of combatants to use force by expanding the definition of civilian targets that were to be off limits to combat. Because of these policies, the United States defied the majority of other nations and refused to ratify the treaty. In his message to the Senate withdrawing AP I, President Ronald Reagan declared that the Protocol was “fundamentally and irreconcilably flawed,” and that its problems were “so fundamental in character that they cannot be remedied through reservations.” He therefore had “decided not to submit the Protocol to the Senate in any form.”21 Chief among these flaws, President Reagan observed, was AP I’s “grant [of] combatant status to irregular forces even if they do not satisfy the traditional requirements to distinguish themselves from the civilian population and otherwise comply with the laws of war.” Reagan recognized the political symbolism of his action, characterizing it as “one additional step, at the ideological level so important to terrorist organizations, to deny these groups legitimacy as international actors.”
AP I demonstrates the pitfalls of replacing the evolutionary approach to war with instant, inflexible legislation. AP I took form before the advent of desktop computers, the Internet, cell phones, global positioning satellites, and cruise missiles. That era’s political circumstances were equally different. Nations were still drafting the text of AP I when North Vietnam conquered South Vietnam. The U.S. and U.S.S.R. dominated world politics and economics, half of Europe was forced into the Warsaw Pact, and the Third World, as it was then known, was still emerging from the throes of decolonization. The collapse of the Soviet Empire, the rise of China, the advent of Islamic extremism, and the spread of global terrorism were yet to come.
Given these significant changes in the world since the mid-1970s, AP I’s provisions are growing hopelessly out of touch with the practice of the states that actually fight wars. Nations themselves realize this. In 1998, for example, a conference in Rome negotiated a treaty to establish the International Criminal Court (ICC).22 Its drafters drew extensively on AP I to define the “war crimes” subject to prosecution. Neither the United States nor other major powers, including Russia, China, India, Turkey, Indonesia, Egypt, Iran, Israel, and Syria, ratified that treaty either. The ICC has so far reached convictions in only a handful of cases, none of them dealing with actions by western armies or with forces outside of Africa.
Nevertheless, AP I remains influential. Even at the time, the United States conceded that much of the treaty merely restated accepted practices.23 It remains the most comprehensive statement of rules for the conduct of military operations. Commentaries on the law of armed conflict, including those by American scholars, assume that provisions of AP I are solid evidence of what the law of war now requires—if not by treaty, then as a matter of “customary law,” which is binding on all states.24
It is important to understand what a significant break AP I is with the history and practice of the law of war. Historically, the laws of war represented customary law, which was established by the actual practice of states over long periods of time. Nations, for example, have long followed a principle of discriminating between combatants and civilians on the battlefield, but had never declared the rule in a general treaty before. States established the rule over centuries through the norms that they consistently followed in wartime. Their applications of the standard of discrimination in different factual circumstances provided guidance for future cases. AP I represents a wholly different approach. It assumes that interested nations can simply legislate the rules of armed conflict by treaty, rather than practice. It assumes that the treatymakers in 1977 could determine the best application of the rules to future circumstances, as opposed to those who fight the wars then.
This view attempts to transform treaty language into instant “custom.” If many states have ratified a treaty, it must represent customary law just as much as, if not more than, universal conduct. Many advocates claim the promises of nations create law more firmly than the practices of nations.25 This is not just an academic exercise, but has become the opinion of international tribunals. For example, the International Court of Justice (ICJ) stated in its 1996 advisory opinion on nuclear weapons, “Extensive codification of humanitarian law and the extent of the accession of the resultant treaties . . . have provided the international community with a corpus of treaty rules the great majority of which . . . reflected the most universally recognized humanitarian principles.” It concluded that IHL treaties, as solidified into custom, “indicate the normal conduct and behaviour expected of States,” presumably whether they had ratified the agreements or not.26 Under this view, the United States can be bound by the rules set out in a treaty it has never ratified because its provisions can be regarded as customary law.27 But those rules remain what they were in the mid-1970s because “customary law” is impervious to contrary practice, even though much military action over the last four decades has not followed AP I.
Domestic analogies reveal the peculiarity of this approach. On domestic statutory questions, courts and executive branch agencies regularly adapt legal principles to fit new factual circumstances. Some of these exercises, of course, can stoke controversy when the application of old legal rules to new technologies is disputed (and disputable). In 2015, for example, the Federal Communications Commission (FCC) prohibited Internet service providers from imposing different charges for carrying different types of content. The FCC subjected Internet service to the same regulatory framework as long-distance telephone service, even though Congress could never have imagined the Internet at the time it enacted the 1934 Federal Communications Act. To be sure, the Commission was divided, as was the U.S. Court of Appeals for the D.C. Circuit, which ultimately upheld the FCC regulation.28 A new majority on the FCC has announced its intention to repudiate the Obama effort to regulate twenty-first century technology with an 80-year-old law.
The tension between adaptation and innovation becomes even more acute when cases turn on the meaning of constitutional provisions now centuries old. The framers of the Bill of Rights could not have envisaged modern technology. It was left to the Supreme Court to decide that First Amendment guarantees
