This comes right back round to where we started.

Think of the governments as companies that produce and enforce the law.  Law providers as such.

If you look at the world as a whole you can see, right now, there is no universal consensus.   We live in an anarchic world populated by what amounts to protection rackets.  

How about instead of these rackets you have several companies that offer security and you can choose which to go with?  One of these stipulations of these companies will be, for example, we will provide you protection from being murdered but if you murder someone then by the terms of the contract you must go to arbitration and accept the judgement.  It's through this process that the laws that you live under are formed.  The company has incentive overall to provide laws that are to the best benefit of the majority of their customers.

Imagine that if these companies that produce law and protect people are 1) No longer confined to any particular territory and 2) They have to attract customers rather than forcibly extracting money from them.   Then you have the same anarchic world where these companies have to interact with each other but customers are free to choose who they want to go with and what level of service they want.   The companies have great incentive to co-operate with each other.  In fact much more so than governments of today, because governments of today can steal vast amounts of money and force people through threat of jail to obey them and kill for them if necessary.   Those dangers don't exist in a voluntary society.