Why is China afraid of the Louisiana Purchase?

Why is China afraid of the Louisiana Purchase?

China Digital Times posts the following leaked government directive which was sent to media companies covering the ongoing anti-Japan protests: 

State Council Information Office: All websites are requested to inspect and clear every forum, blog, Weibo post and other form of interactive content of material concerning “mobilizing , stirring up excitement, rioting and looting” and “the history of purchasing territory.” (September 15, 2012)

That last one seems a bit out of place. Why are authorities worried about Chinese netizens reading about Seward’s icebox and and the Gadsden Purchase? Is there a fear that these purchases are somehow a precedent for the Japanese government’s purchase of three of the disputed Senkaku/Diaoyu islands?

The two situations aren’t quite comparable. The United States has, on several occasions in its history, paid to acquire territory previously held by foreign powers. The Japanese government, on the other hand, was buying land it already considered Japanese territory from its private owners — mostly to prevent Tokyo’s hardline nationalist governor from doing it first. 

As I wrote in a post back in June, the buying and selling of territory between states is a lot less common than it was in the days when European powers held vast overseas empires and there was significantly more terra nullius to be claimed. (Actually the closest thing to it these days are state-affilated Chinese conglomerates buying Luxembourg-sized chunks of Argentinian farmland.)

On the other hand, given how many territorial disputes China is involved in at the moment, a study of how these conflicts have been resolved peacably in the past might not be a terrible idea.