Well, you have to worry about the dollar becoming worthless.
Because back in WWII, the thing that really sparked the Japanese was the feeling the only way to get was to take.
Currently the world is operating under a monetary acquisition system, you can have anything as long as you have the money. If all of a sudden your money is worthless, the danger is countries will revert back to the former model.
In that case, yes China would try to use her military might to acquire that which she desires.
Plus Obama promised China in February 2009 that if we were unable to pay back our debts, we would give them land/assets. He said it to get them to resume their buying of treasuries. Whether or not it’s true that he will actually try to give them our assets, if the economic situation goes south, they’ll still be miffed. I don’t see the average American buying into that plan.