[b]The Neo United Nations[/b]

The Neo - or New - United Nations was formed in the wake of the Heavenfall. After the Cold War and the Heavenfall, the former United Nations no longer seemed adequate in the face of global devastation and the realities of the new, more dangerous and more unsettled post-Heavenfall world. Ideologies grated against one another, and the endless disagreements in policies and ideas had served only to reduce the United Nations as an organisation into something of a pointless exercise in bureaucracy. 
As the former leading nations of the Northern Hemisphere rebuilt and reorganised, it fell to those still prosperous in the South to reorganise and forge a new path. 
The model of the original United Nations was taken as an example, but this new organisation would be more decisive, more pro-active, and wield more firm authority. It's decisions would be binding and implemented universally, and it would be more of a shared group of policies and alliances, rather than a participatory body. Not quite a global or world government, but certainly a step on the road towards one, and for setting a global standard of living, safety, security and well-being for all of those nations that were members. 
N/UN policies revolve around human rights and equality for race, sex, gender and sexuality, equality for wages and fair pay, employment, education, medicine and healthcare, as well as fair and free trade agreements, stable, honest and fair government, and an otherwise high and developed standard of living for all citizens. The N/UN also enables and sponsors several international initiatives, such as co-operation for international law enforcement, trade agreements, and travel between N/UN member states, as well as international recognition of educational achivements and qualifications.

Individual member countries still maintain their autonomy, still elect their own officials, trade in their own currencies, maintain their own borders, and other such marks of free nations. However, in return for mutual aid, security, and other benefits, they would also have to maintain standards of human rights, politicial and individual freedoms and other such 'standards'. 
The benefits of being part of the alliance served as a kick-starter for reform for some countries and groups, while others rejected the idea, withdrawing from it and pursuing their own alliances instead - leading to the NCAA, ISL, CAA and so on being formed. 

As the Northern nations rebuilt, they were offered membership as a legacy from their parts in the Western powers against the Eastern Bloc, as well as from having been part of the original UN. Almost all of them accepted, and have contributed to the international alliance.

With so many fires to fight on so many fronts, and being such a large and unwieldy organization, the N/UN may be powerful, but it can take a long time for it to mobilise into action - despite being intended to be swift, decisive and powerful, there are still debates and consensus of action to be reached, all of which takes considerable time and effort to achieve. 

As such, the N/UN organised and enacted the legalisation and support of approved and vetted Private Military Contractors. 
PMC's given authorisation by the N/UN were allowed to possess military-grade weapons, vehicles, and equipment equivalent to modern national military forces, although there were still strict limits on the types of weapons they could and could not use, and restrictions on their overall size, to prevent them from exceeding the ability of the N/UN itself to control them. 

The N/UN has invited various other nations to join the Alliance, but some have refused or maintained their own sovereignty, either for peaceful or hostile reasons. Others have various treaties and agreements with the N/UN that are of mutual benefit and interest. 
The N/UN general assembly and headquarters is in Canberra, Australia.