Of all the countries on Earth, there are only really two that could mount a full scale invasion against the United States and hope to win, China and Russia. Neither is likely, but it would have to be one of them for us to consider this scenario.

Also, you're right that China invading the US is probably very unlikely, but probably not for any historical reasons. China and the US rely on each other too much as trading partners at this juncture for a full scale war to be wise. Also, much of China's wealth is wrapped up in US debt, a war with the US would endanger their savings. The biggest contention between the US and China at this point is the independence of Taiwan, which could lead to war, but not a mainland invasion of the United States.

Then again, if you do look at history, Japan's attack on Pearl Harbor was motivated by passive aggressive attempts by the United States to 'contain' Japan during the Second World War. Specifically, the United States blocked the import of oil to Japan. If the United States tries too hard to contain China, China might feel compelled to break the US's hold on the Pacific. This isn't like though, and a full scale war coming of it is also unlikely.