Customary international law increasingly being forced to adapt quickly to technology

Custom can also develop rapidly based upon interpretations of treaties, as well as the rulings and declarations of international bodies and courts that can declare an existing customary rule.⁸⁷ In the past 50 years, customary rules have developed quickly in response to technological innovation or in times of fundamental change.⁸⁸ Moreover, rapid changes to custom do not require multiple instances of state practice,⁸⁹ particularly when a state with special influence in the field seeks change.⁹⁰ Most recently, the terrorist attacks on the World Trade Center and Pentagon resulted in changed custom concerning the use of force in self-defense against non-state actors⁹¹ and those who support or harbor terrorists.⁹² Such changes to the well-settled field of international humanitarian law would have been unthinkable in an earlier era.