* Firstly, who's to tell Liblanders that they risk invasion? It's not clear that Libertarianism supports the notion of foreign policy, diplomacy, espionage etc.
* Secondly, all the food in the country is coming from Xia. Once demand grows Xia realises that Libland has recognised the threat and invades immediately.
It is entirely clear that Libertarianism does support those things and one of the two roles of a Libertarian government is the physical security of the nation and its citizens.
Now, a worthy chap sees a report about Xia on CNN and gets suspicious. How's he going to get enough money to mount a publicity campaign warning Libland citizens of the danger?
Just like 9-11, Dec 7, 1941, the anschluss, mongol invasions...the Hitties and Philistines versus the Israelites, yeah, military ops are always telegraphed.
"War between Japan and the United States had been a possibility each nation had been aware of (and developed contingency plans for) since the 1920s" - http://en.wikipedia.org/wiki/Attack_on_Pearl_Harbor#Backgrou...
"Austria was merged into Nazi Germany on 12 March 1938. There had been several years of pressure from Germany and there were many supporters within Austria for the "Heim ins Reich"-movement, both Nazis and non-Nazis." - http://en.wikipedia.org/wiki/Anschluss
Your less specific in the details of your other facts so it's hard to get specific counter-facts on them.