Hypothetical situation: the Internet gets split in two, what happens with Bitcoin? Let's suppose, that at some time the Internet gets split in two, possibly because of wartime, or another possibilities (there was once a situation, when Egypt managed to split the internet in their country from the outside).


There begins to exist two versions of the blockchain, eg. USACoin and ChinaCoin
There are some people with access to both internets ("pirate joins")
Eventually, the internets join back


How would Bitcoin software react to those splits, how would it react to the "pirate joins", how would it handle the final internet join? What would be the "Plan B" of the Bitcoin community?
Any of the "pirates" with nodes on both networks and who have unspent coins in the blockchain before the split would be able to spend those on both networks, for as long as the network is split. 

Upon joining again, the longest chain will always prevail. So anyone who mined any new coins after the split and those were mined on the shorter of the two chains will lose all those new coins -- they will become invalid. 

Anyone who spent coins that existed before the split, but spent them only on the shorter chain, will have those coins returned to him/her after the join, because they were only spent on the shorter chain (which is discarded and invalidated)

In short, the bitcoin network will take it in stride :) but some people will lose, and some will benefit doubly.