 On the evening of the 12th September 2001, less than 24 hours after the 9-11 terrorist attacks in the United States, NATO came to a consensus to invoke Article 5 of the Washington Treaty, stating that an attack on one member of the Alliance is an attack on all members. It was the first time that Article 5 had been invoked and had put in motion a range of international counter-terrorism operations. It was the first time that NATO military assets had been deployed as a collective response to an external threat. NATO is a consensus decision-making organisation, so the Alliance cannot act if one of its member countries objects to a course of action being considered. The invocation of Article 5 after 9-11 was perhaps the most famous consensus decision made by NATO. On the flip side, for example, for many years, Greece blocked a NATO decision to let in the former Yugoslav Republic of Macedonia until it changed its name to North Macedonia, which occurred in 2018. Alliance funding is based on direct and indirect contributions. Direct contributions serve the interests of all member countries and fund NATO-wide commands. Each member's direct contribution is proportional and formulated using a common funding principle based on each member state's gross national income using an agreed formula. However, the largest contributions are indirect, encompassing such things as members' voluntary provision of military forces and equipment to operations and the assignment of multi-personnel or diplomats to work at NATO itself. The costs lie where they fall, principle. The question of burden-sharing in NATO has been debated for years, both during and since the Cold War. Some member countries perceive others as not allocating a sufficient amount of their government spending on defence. Following the Russian seizure of Crimea in 2014, the NATO Allies pledged at the Wales Summit to move towards spending 2% of GDP on defence by 2024 with 20% of that to be spent on major equipment. NATO comprises various formal bodies that are responsible for different aspects of decision-making and the provision of advice to decision-makers. The North Atlantic Council is the principal political decision-making body in NATO, taking final decisions as necessary on all issues. It meets at ambassadorial, ministerial and head-of-state and government levels with weekly meetings or when needed, for example, during periods of crisis. The Secretary General of NATO is historically a European politician or diplomat and is supported by several other senior appointees, as shown in the table. All member countries maintain permanent delegations at NATO's political headquarters in Brussels, led by an ambassador and which represent their governments in alliance, consultation and decision-making. There are two principal committees in NATO. In addition to the North Atlantic Council, the Military Committee is NATO's senior military authority and the primary source of military advice to NATO's civilian decision-making bodies. The advice of the Military Committee is sought prior to any authorisation of military action and so it represents an essential link between the political decision-making process on one hand and the military structures of NATO on the other. The nuclear planning group acts as the alliance's senior body on issues related to nuclear forces. Its discussions cover the safety, security and survivability of nuclear weapons, communications and information systems, deployment issues, nuclear arms control and proliferation. It has the same authority as the North Atlantic Council with regard to nuclear policy issues. Within NATO, reporting committees are specialised agencies which provide advice to the North Atlantic Council and the nuclear planning group on specific topics. The international staff provides advice, guidance and administrative support to the national delegations at NATO headquarters in order to help implement decisions taken at different committee levels. Dialogue councils are the institutions of cooperation, partnership and dialogue that underpin relations between NATO and other countries. NATO centres of excellence are NATO accredited independent international military organisations that train and educate leaders and specialists from NATO member and partner countries. Notable examples include the Strategic Communication Centre of Excellence in Riga, Latvia, the NATO Co-operative Cyber Defence Centre of Excellence in Tallinn, Estonia and the Defence Against Terrorism Centre of Excellence in Ankara, Turkey. NATO committee structures are avowed periodically to keep pace with priorities and to make the alliance more efficient and responsive. There have been three major committee restructures since 1949, in 1990 after the end of the Cold War, in 2002 after the terrorist attacks of 9-11 and more recently in 2010 to help the alliance to respond more effectively to security challenges and to adopt more integrated, flexible working procedures. In summary then NATO is a consensus-based decision-making organisation. The North Atlantic Council is the alliance's principal political decision-making body and is supported by the military committee when decisions relate to military issues. The nuclear planning group is the senior body on nuclear issues and has the same authority as the North Atlantic Council on nuclear questions. NATO is funded through both direct and indirect funding contributions. In 2014 the member countries pledged to spend 2% of their GDP on defence by 2024.