On 19 December 2005, in its partial award, the Eritrea-Ethiopia Claims Commission found that Eritrea had acted in violation of the rules of international law on the use of force (jus ad bellum) in resorting to armed force to attack and occupy the disputed border town of Badme and surrounding areas, which were then under the peaceful administration of Ethiopia. In its award, the Claims Commission made a number of important findings which, taken with the Eritrea-Ethiopia Boundary Commission's 2002 decision on boundary delimitation, contribute towards informing and clarifying the substance of international law applicable to disputed territories and the legal obligations of states acting in those areas, especially where the use of force is engaged. This article examines the Claims Commission's jus ad bellum award and concentrates on three key issues: a) the legality in international law of the resort to force as a means of gaining control over territory to which a state has (or believes that it has) a valid sovereignty title; b) the specific contours of self-defence in relation to territorial sovereignty claims, and c) the legitimacy of dealing with use of force issues by arbitral tribunals. In September 2018, the leaders of the two countries signed a peace and friendship agreement, thus, setting course for a new era of peace and cooperation. The lessons that ought to be learnt by these two neighbouring countries and other states have been articulated as concluding remarks. 1 The Kingdom of Aksum existed during the first seven (although others submit nine) centuries AD in Northern Ethiopia. Its rule and power influence encompassed modern Yemen, Somalia and Djibouti. It adopted Christianity in the 4 th Century AD, introduced, and used its own language called Ge'ez. This ancient civilisation was a dominant trading empire in the Red Sea until the end of the ninth century, see Phillipson (1998) 1-55. 2 General Assembly Resolution 390A(V) (2 December 1950) https://documents-ddsny.un.org/doc/RESOLUTION/GEN/NR0/059/88/IMG/NR005988.pdf?OpenElement 3 On the history of the Ethiopian region see Marcus (2002); Zewde (1998). 4 The Declaration called upon Eritrea 'immediately' and 'unconditionally' to withdraw its army from Ethiopian controlled territories, 'Letter dated 20 December 2005 from the Charge d'affaires a.i. of the Permanent Mission of Ethiopia to the United Nations addressed to the President of the Security Council' 3 . 5 The war lasted two years and involved the deaths of 70,000 soldiers and the displacement of over a million civilians. Government spending had been diverted to the arms race. Drought and famine seriously aggravated the situation causing a large humanitarian crisis, Gray (2006) 702-704; In addition, one of the consequences of this conflict was its spillover effect on the