Rule 2. Violence Aimed at Spreading Terror among the Civilian Population
Rule 2. Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited.
Summary
State practice establishes this rule as a norm of customary international law applicable in both international and non-international armed conflicts.
International armed conflicts
Article 51(2) of Additional Protocol I prohibits “acts or threats of violence the primary purpose of which is to spread terror among the civilian population”.[1]  No reservations have been made to this provision. At the Diplomatic Conference leading to the adoption of the Additional Protocols, Mexico stated that Article 51 of Additional Protocol I was so essential that it “cannot be the subject of any reservations whatsoever since these would be inconsistent with the aim and purpose of Protocol I and undermine its basis”.[2]  Also at the Diplomatic Conference, the United Kingdom stated that Article 51(2) was a “valuable reaffirmation” of an existing rule of customary international law.[3] 
The prohibition of acts or threats of violence aimed at terrorizing the civilian population is set forth in a large number of military manuals.[4]  Violations of this rule are an offence under the legislation of numerous States.[5]  The prohibition is also supported by official statements.[6]  This practice includes that of States not, or not at the time, party to Additional Protocol I.[7]  States party to Additional Protocol I have also invoked this rule against States not party.[8] 
When the ICRC appealed to the parties to the conflict in the Middle East in October 1973, i.e., before the adoption of Additional Protocol I, to respect the prohibition of “methods intended to spread terror among the civilian population”, the States concerned (Egypt, Iraq, Israel and Syria) replied favourably.[9] 
It can be argued that the prohibition of acts or threats of violence aimed at terrorizing the civilian population is further supported by the wider prohibition of “all measures of intimidation or of terrorism” in Article 33 of the Fourth Geneva Convention.[10]  Prior to the adoption of this provision, the Report of the Commission on Responsibility set up after the First World War listed “systematic terror” as a violation of the laws and customs of war.[11] 
Non-international armed conflicts
Article 13(2) of Additional Protocol II prohibits acts or threats of violence the primary purpose of which is to spread terror among the civilian population.[12]  In addition, the prohibition is included in other instruments pertaining also to non-international armed conflicts.[13] 
The prohibition of acts or threats of violence aimed at terrorizing the civilian population is set forth in military manuals which are applicable in or have been applied in non-international armed conflicts.[14]  Violations of this rule in any armed conflict are an offence under the legislation of many States.[15]  There are also official statements pertaining to non-international armed conflicts invoking this rule.[16] 
It can be argued that the prohibition of acts or threats of violence aimed at terrorizing the civilian population is further supported by the wider prohibition of “acts of terrorism” in Article 4(2)(d) of Additional Protocol II.[17]  “Acts of terrorism” are specified as war crimes under the Statutes of the International Criminal Tribunal for Rwanda and of the Special Court for Sierra Leone.[18]  In his report on the establishment of a Special Court for Sierra Leone, the UN Secretary-General noted that violations of Article 4 of Additional Protocol II have long been considered violations of customary international law.[19] 
No official contrary practice was found with respect to either international or non-international armed conflicts. Alleged violations of this rule have generally been condemned by States.[20]  Similarly, the UN General Assembly and UN Commission on Human Rights have adopted several resolutions condemning the terrorization of the civilian population in the conflicts in the former Yugoslavia.[21]  Furthermore, the indictments in the Đukić case, Karadžić and Mladić case and Galić case before the International Criminal Tribunal for the Former Yugoslavia included charges of terrorizing the civilian population in violation of the laws and customs of war, in the first two cases as part of charges of unlawful attack.[22]  In its judgment in the Galić case in 2003, the Trial Chamber found the accused guilty of “acts of violence the primary purpose of which is to spread terror among the civilian population, as set forth in Article 51 of Additional Protocol I, as a violation of the laws or customs of war under Article 3 of the Statute of the Tribunal”.[23] 
The ICRC has reminded parties to both international and non-international armed conflicts of the prohibition on terrorizing the civilian population.[24] 
Examples
Examples of acts of violence cited in practice as being prohibited under this rule include offensive support or strike operations aimed at spreading terror among the civilian population,[25]  indiscriminate and widespread shelling,[26]  and the regular bombardment of cities,[27]  but also assault, rape, abuse and torture of women and children,[28]  and mass killing.[29]  The indictments on the grounds of terrorizing the civilian population in the above-mentioned cases before the International Criminal Tribunal for the Former Yugoslavia concerned deliberate and indiscriminate firing on civilian targets,[30]  unlawful firing on civilian gatherings,[31]  and a protracted campaign of shelling and sniping upon civilian areas.[32]  These examples show that many acts violating the prohibition of acts or threats of violence aimed at terrorizing the civilian population are also covered by specific prohibitions.

[1] Additional Protocol I, Article 51(2) (adopted by 77 votes in favour, one against and 16 abstentions) (cited in Vol. II, Ch. 1, § 477).
[2] Mexico, Statement at the Diplomatic Conference leading to the adoption of the Additional Protocols (ibid., §§ 146, 307, 536 and 800).
[3] United Kingdom, Statement at the Diplomatic Conference leading to the adoption of the Additional Protocols (ibid., §§ 319, 537 and 803).
[4] See, e.g., the military manuals of Argentina (ibid., § 489), Australia (ibid., § 490), Belgium (ibid., §§ 491–492), Benin (ibid., § 493), Cameroon (ibid., § 494), Canada (ibid., § 495), Colombia (ibid., § 496), Croatia (ibid., § 497), Ecuador (ibid., § 498), France (ibid., § 499), Germany (ibid., § 500), Hungary (ibid., § 501), Kenya (ibid., § 502), Netherlands (ibid., § 503), New Zealand (ibid., § 504), Nigeria (ibid., § 505), Russia (ibid., § 506), Spain (ibid., § 507), Sweden (ibid., § 508), Switzerland (ibid., § 509), Togo (ibid., § 510), United States (ibid., §§ 511–512) and Yugoslavia (ibid., § 513).
[5] See, e.g., the legislation of Argentina (ibid., § 514), Australia (ibid., § 515), Bangladesh (ibid., § 516), Bosnia and Herzegovina (ibid., § 517), China (ibid., § 518), Colombia (ibid., § 519), Côte d’Ivoire (ibid., § 520), Croatia (ibid., § 521), Czech Republic (ibid., § 522), Ethiopia (ibid., § 523), Ireland (ibid., § 524), Lithuania (ibid., § 525), Netherlands (ibid., § 526), Norway (ibid., § 527), Slovakia (ibid., § 528), Slovenia (ibid., § 529), Spain (ibid., § 530) and Yugoslavia (ibid., § 531).
[6] See, e.g., the statements of Israel (ibid., § 534), Lebanon (ibid., § 535) and United States (ibid., §§ 538–540).
[7] See, e.g., the practice of France (ibid., § 499), Israel (ibid., § 534), Kenya (ibid., § 502) and United States (ibid., §§ 511–512 and 538–540).
[8] See, e.g., the statement of Lebanon vis-à-vis Israel (ibid., § 535).
[9] See ICRC, The International Committee’s Action in the Middle East (ibid., § 556).
[10] Fourth Geneva Convention, Article 33 (ibid., § 476). The relevance of this provision to the present rule is explained in Yves Sandoz, Christophe Swinarski, Bruno Zimmermann (eds.), Commentary on the Additional Protocols, ICRC, Geneva, 1987, § 4538.
[11] Report of the Commission on Responsibility (cited in Vol. II, Ch. 1, § 481).
[12] Additional Protocol II, Article 13(2) (adopted by consensus) (ibid., § 479).
[13] See, e.g., Memorandum of Understanding on the Application of IHL between Croatia and the SFRY, para. 6 (ibid., § 485); Agreement on the Application of IHL between the Parties to the Conflict in Bosnia and Herzegovina, para. 2.5 (ibid., § 486).
[14] See, e.g., the military manuals of Argentina (ibid., § 489), Australia (ibid., § 490), Benin (ibid., § 493), Cameroon (ibid., § 494), Canada (ibid., § 495), Colombia (ibid., § 496), Croatia (ibid., § 497), Ecuador (ibid., § 498), Germany (ibid., § 500), Hungary (ibid., § 501), Kenya (ibid., § 502), Netherlands (ibid., § 503), New Zealand (ibid., § 504), Russia (ibid., § 506), Spain (ibid., § 507), Togo (ibid., § 510) and Yugoslavia (ibid., § 513).
[15] See, e.g., the legislation of Bosnia and Herzegovina (ibid., § 517), Colombia (ibid., § 519), Croatia (ibid., § 521), Ethiopia (ibid., § 523), Ireland (ibid., § 524), Lithuania (ibid., § 525), Norway (ibid., § 527), Slovenia (ibid., § 529), Spain (ibid., § 530) and Yugoslavia (ibid., § 531); see also the legislation of the Czech Republic (ibid., § 522) and Slovakia (ibid., § 528), the application of which is not excluded in time of non-international armed conflict, and the draft legislation of Argentina (ibid., § 514).
[16] See, e.g., the statements of Botswana (ibid., § 533) and United States (ibid., § 540).
[17] Additional Protocol II, Article 4(2)(d) (adopted by consensus) (ibid., § 478). The relevance of this provision to the present rule is explained in Yves Sandoz, Christophe Swinarski, Bruno Zimmermann (eds.), Commentary on the Additional Protocols, ICRC, Geneva, 1987, § 4538.
[18] ICTR Statute, Article 4(d) (cited in Vol. II, Ch. 1, § 487); Statute of the Special Court for Sierra Leone, Article 3(d) (ibid., § 480).
[19] UN Secretary-General, Report on the establishment of a Special Court for Sierra Leone (ibid., § 545).
[20] See, e.g., the statements of Israel (ibid., § 534), Lebanon (ibid., § 535) and United States (ibid., § 540).
[21] See, e.g., UN General Assembly, Res. 49/196 (ibid., § 541) and Res. 53/164 (ibid., § 542); UN Commission on Human Rights, Res. 1992/S-2/1, 1993/7, 1994/72 and 1995/89 (ibid., § 543).
[22] ICTY, Đukić case, Initial Indictment (ibid., § 551), Karadžić and Mladić case, First Indictment (ibid., § 553) and Galić case, Initial Indictment (ibid., § 554).
[23] ICTY, Prosecutor v. Stanislav Galić, Case No. IT-98-29-T, Judgment and Opinion, 5 December 2003, § 769.
[24] See, e.g., the practice of the ICRC (cited in Vol. II, Ch. 1, §§ 556–558 and 561).
[25] Australia, Defence Force Manual (ibid., § 490).
[26] UN General Assembly, Res. 53/164 (ibid., § 542).
[27] UN Commission on Human Rights, Special Rapporteur on the Situation of Human Rights in the Former Yugoslavia, Report (ibid., § 546).
[28] UN High Commissioner for Human Rights, Report on systematic rape, sexual slavery and slavery-like practices during armed conflicts (ibid., § 547).
[29] OSCE, Kosovo/Kosova, as seen as told, An analysis of the human rights findings of the OSCE Kosovo Verification Mission (ibid., § 549).
[30] ICTY, Đukić case, Initial Indictment (ibid., § 551).
[31] ICTY, Karadžić and Mladić case, First Indictment (ibid., § 553).
[32] ICTY, Galić case, Initial Indictment (ibid., § 554).