2.1. Facts: In 2014, Houthi rebels in Yemen - allegedly supported and armed by Iran- were advancing throughout the country, eventually taking Yemen's capital Sanaa. After initially resigning from his post but then later retracting his resignation, Yemeni President Hadi fled to neighbouring Saudi Arabia in March 2015. After arriving there, Hadi invited Saudi Arabia and allied states to intervene to stop the Houthi rebels: "I ask you, based on the principle of self-defence in Article 51 of the Charter of the United Nations... to provide instant support by all necessary means, including military intervention to protect Yemen and its people from continuous Houthi aggression....". Shortly thereafter, and citing Hadi's invitation to intervene as well as pre-emptive self-defence against the threat posed by the Houthis to the whole region. Saudi Arabia in concert with other states launched a military intervention in Yemen to stop the Ilouthi advances. This led to a long military confrontation in Yemen. The UN Security Council has not authorised the intervention. Analyse this situation from a use of force perspective and refer to relevant international legal sources to support your analysis. Does Saudi Arabia's intervention in Yemen constitute a lawful use of force under international law? 2.2. Additional developments: In September 2019, Saudi Arabia's Abqaiq petroleum facility was attacked by drones. Abqaiq is one of the largest processing plants in the world. The facility is located in castern Saudi Arabia, near the Persian Gulf. The drone attack damaged several of the plant's stabilization towers, which are used to remove impurities from crude oil. This resulted in a significant increase in global oil prices and had a considerable economic impact on countries across Asia and Europe, which heavily rely on Saudi oil. The Houthi rebels in Yemen claimed responsibility for the attack. Saudi Arabia also blamed involvement of Iran citing evidence from recovered drone parts. Iran denied involvement in the attack. Analyse this situation from a use of force perspective and refer to relevant international legal sources to support your analysis. Would Saudi Arabia be entitled to use force in self-defence under international law?