The only way it would be possible for the entire human race to come together is if everyone could be convinced to accept the same [i]ideology[/i].  This is a complete [i]impossibility[/i] for many reasons, one easily identifiable reason being the idea that all ideas and ideologies are equally viable.  Even people who claim everyone is equal probably don't actually believe it hence, according to that that logic even a racial supremacist has an equal view to a nihilist or whatever ideology you want to put out there.

Diversity is not strength when the members of that diversity are completely [i]opposed[/i] to each other.  Tolerance has become intolerance and everything has quickly come full circle around to exactly the same problems humanity has been dealing with for all time.  For there to even be the remotest possibility for all of humanity to come together, there has to be some kind of unifying ideology for the people to follow, otherwise differences of opinion will [i]inevitably[/i] lead to conflict.

As annoying as it might be to admit, the ideologies closest to bringing people together have been and will always be, Religion[that being said there are a lot of 'religions' that cannot do this or are even exclusionary because of the beliefs they hold].  The reason why Religion is, and always will be, the best chance for humanity to come together is because it makes people come together with an easily identifiable foundation like a god.

Of course, I'd say it is safe to say that like any ideology as soon as it gets too big and bulky it starts to be abused by [i]people[/i].  Every ideology that attempts to create a global community is doomed to fail because of the humans who try to use it, maybe the ideology is right in what it is trying to accomplish but the execution will always be faulty due to human error, negligence, greed, etc.  A world without borders, without killing, without opposing viewpoints is impossible, unless there is some outside force that can straighten things out.

Like it or not, Religions will always exist on this Earth as most people feel that the Earth is way too crazy to ever become a paradise without some external force to right things.  Of course, even though it is probably impossible to get everyone on Earth to agree to get along, at the very least don't be part of the problem and do your best to help out.

If you could find a way for Christians, Muslims, and Atheists to exist peacefully together then maybe there would be a chance for world peace.  Oh, but then I'd be forgetting the Buddhists, Taoists, Satanists, Shintoists, Judaists, Catholics[as some Christians consider them to be separate from Christianity], Deists, Hindus, and of course all the different sects of all the different religions in the world.  People either learn to live with each other or reject each other and because certain ideologies are naturally enemies of the other, rejection will and does happen on a regular basis.

Until a single Ideology/Religion can be shared by all of humanity it is impossible to bring the Earth together, at least in a peaceful way...I for one do not want to see anyone subjected to any kind of tyrannical ideology or government that tries to impose its views on everyone else.

Oh and until North Korea is saved from its evil dictator, there can never be true peace on the Earth XD.

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I don't blame anyone who didn't bother to read the whole thing.  The short and quick is humanity can only be brought together if everyone can accept a single ideology.  Also the only likely way for that to happen is through the power of some outside force like God.  Best thing we can do as individuals is to help out and be kind and considerate to our fellow man rather than trying to [i]force[/i] our ideas on others, if you think your way of thinking is a better way then by all means, share it so people can discuss it and decide for themselves.