Again, the right of self defense would come into play. Shameful it if ever happened. War sets everybody back.
And here's already an example of how "righteous" societies often fail (google "kondratieff cycles"). Trough just laws you amass great wealth. To protect it, you develop great power. And finally, you start using power for economic gain (It is precisely why founding fathers warned us about the danger of standing armies)
Note that the adoption of a doctrine permitting the use of power for economic gain could be entirely market driven. The market sees the army as an under-utilized resource and tries to optimize its use. If the army is defensive in nature, events will be manufactured to provoke "defensive actions", leading to more optimal utilization of the asset (army).
The conscious use of force for economic gain trickles down to all aspects of life, undermines the moral strengths of the laws (legal is no longer considered just) and leads to poverty & decay.
So even if Libertarian society is established and if it becomes very prosperous and if it develops great power to defend its prosperity, the ultimate challenge would be preserving its character and not succumbing to Kondratieff cycles.