The United Nations is one of the greatest achievements of the 20th century, and indeed in all of human history: A permanent, standing diplomatic body with virtually universal recognition where the nations of the world can work out their differences peacefully, cooperate for mutual benefit, and deliver humanitarian assistance when and where necessary. No one can deny the profound and lasting change its existence has had on geopolitics, making Total War a thing of the past, heading off nuclear Armageddon among the Cold War superpowers, and creating a level of global stability never even imagined before the modern era. But while the UN has excelled at the tasks for which it was designed, it can never be effective as what its critics often justly accuse of it failing to be - a universal democratic body committed to pursuing global political freedom. So I ask, why not form such a body?
Here's the truly brilliant part of the concept: We The People of The World need no one's permission to form such a body, at least in most countries - no governmental approval is necessary to form and participate in an international NGO consisting of freely elected representatives and budgets based on contractually-obligated periodic donations (as opposed to taxes) in exchange for having a vote. And since the whole point of the organization is to promote freedom and democracy on a global scale, the absence of representatives from countries where the people have no practical ability to associate and vote freely is simply an accurate assessment of where the balance of freedom stands in the world. In other words, it's a feature, not a bug - and one that needn't be absolute since expatriate communities would still be able to send representatives of their people in exile.
While the UN is often rightly criticized for putting criminal dictators on an even diplomatic footing with democracies, this is a necessity of what that body was created to accomplish: Achieve peace and stability between nations, and coordinate humanitarian aid to address the consequences of wars, chaotic situations, and natural disasters that do occur. It does both of these things better than anything else has ever done them before, but there is a glaring (and necessary) gap in this arrangement: In exchange for its ability to bring peace, the UN is incapable of promoting internal change within powerful member states regardless of their political system or human rights record. This was the unavoidable compromise that went into the UN Charter in placing the Soviet Union (now Russia) and China on the permanent Security Council, with un-overridable veto powers over any UN resolution.
But even if every single member state were democratic, the UN still would not be - as far as I know, not a single one of its delegates is directly elected by the citizenry of a member state, so in effect the name of the body is a misnomer: The nations of the world are not "united" in any way, shape, or form by such a body, nor can they ever be - they are not even loosely confederated. And the reason is the same one that troubles the European Union to a lesser extent - there is no sociopolitical foundation to any of it. It is a superficial construction tenuously webbed through the world's diplomatic bureaucracies and little else - neutral ground where states run by killers and thieves debate minutiae with their victims, critics, and accomplices. We still need that, but it's not enough anymore.
So I would like to throw this idea out there for further consideration, and recommend the following:
1. That a suitable catalyst organization be identified or formed with the purpose of creating a directly-elected international body. This organization should be of a size, stature, and credibility suitable for the difficulty and complexity of the task, and with a superb record of integrity.
2. That the body ultimately created be funded from progressively-scaled, ironclad contractual obligations to donate in exchange for having a vote in the body. This would be effectively the same as taxes for those who choose to participate, and the fact that the obligation would be progressive would assure equal access. Moreover, the fact that the contract would be long-term assures that, should it ever become powerful enough to attract such interest, the wealthy would not be able to game the system by buying access when convenient and then ditching the organization when not.
If the effort succeeded, the voluntary nature of participation would give rise to a free-rider problem in the early years, but over the longest term, explicit taxation via national governments and official recognition of representation would likely follow. That is the pattern of history: Effective laws are only created to codify and regularize developments already occurring in society - they cannot fly in the face of the society being governed, and any attempt to do so is always doomed to destroy the credibility of whatever authority tries. In other words, governments would lend explicit authority to an elected global body only when such a body already exists and already has established social authority - but they will never create such a thing of their own initiative.
3. The organization would then establish a framework for holding elections among the founding members to appoint representatives to write a Constitution or charter for the global body - something rigorous, with teeth, that embodies the values of the Universal Declaration of Human Rights but combined with a missionary zeal to promote, protect, and defend them in practice regardless of diplomatic or economic interests. It should also have impeccable checks and balances, and yet the flexibility to respond to changing circumstances.
4. The ultimate body would consist of elected representatives, although the particulars of how many, how large the constituencies would be, and what sort of legislative structure would be undertaken would be left to the political architects who create the Constitution. It need not start right off the bat with people from every part of every eligible country if not immediately practical - just a handful of the most "important" and/or most eager, and then expand steadily from there.
5. The body, once in operation, would decide what to do with the money it collects in pursuit of the objectives laid out in the founding document. Among these would obviously be: Human rights, free and fair democracy, equality of opportunity, science, global environmental protection, civil rights, etc. - basically a thorough but succinct statement of a broad-based liberal/progressive agenda.
6. It would aggressively pursue these values on every occupied square inch of the planet within its practical reach, and deliberately antagonize oppressive or borderline states in order to expose the true extent of the problem. Remember, this is not supposed to be the UN - not a diplomatic body that attempts to pursue change in oblique whispers. But rather an assertive body that, for the first time in human history, would seek to bring the voice of the people to the global stage on an explicit basis.
7. If it managed to become significant, I would imagine the attitude of global governments to it would be what Gandhi said: First they ignore you, then they laugh at you, then they fight you, then you win. At first it would be perceived as what it is - a hugely ambitious, perhaps impractical effort by idealists to internationalize democracy. If it managed to continue and grow, its initial successes would be very modest compared to the boldness of its vision, so it would be easy for people in government and diplomacy to regard it as some kind of silly, impotent farce for naive humanitarians and activists.
But with continued growth, eventually it would become a thorn in the side of existing power - e.g., if it pissed off China and had them complaining to the US about these "crazy subversives" - which might result in the kind of petty authoritarian crap that usually comes at anything that annoys real power. If it got that far, it would already be too late to stop, and eventually it would simply usurp the moral authority - and thus, inevitably, political power - of individual Western governments and the UN. Probably take generations though, if it succeeded at all. But it's definitely worthwhile.
The simple fact is that existing institutions are utterly failing to address the challenges of the 21st century in a timely, organized, and effective manner: National governments are complacent, unaccountable, and corrupt; radical movements are either brutal and degenerate or nebulous and incapable of rational prioritizing; and today's international bodies are either virtually impotent beside the interests of their most powerful constituent states or exist solely to serve the rich and the corporate bureaucracies they control (e.g., the World Bank). Climate change, resource depletion, poverty, economic inequality, political oppression...to deal with these challenges, we have to fundamentally up the ante on democracy and global scientific leadership, and if nations won't do it; if the UN can't do it; and if corporations don't give a shit, then it seems this is the answer: World Congress. No existing authority's permission or help is needed to get the ball rolling on it.