Ironically, I recall that in Frank Capra's The Battle of China (part of the "Why We Fight" series) it was claimed that in all their history the Chinese had never engaged in a war of conquest. Wartime propaganda, I suppose.
Old wine in new bottles. British commanders were extremely wary of the presence of Chiang's armies in Burma (then part of the British empire occupied by Japan) during WWII, given the Chinese claim on the entire territory as a tributary state (a la Tibet). Sinologists are not to be trusted on the subject of China's territorial acquisitiveness - too many fall in love with their subject, in some cases, literally, by marrying Chinese spouses. They're not entirely to be blamed, of course. Anyone who spends a lifetime researching a given subject is likely to have an unusual degree of attachment to it, coupled with an inability to see its warts for what they are.
One final question: if Chiang had won the Civil War instead of Mao, would China still be our enemy?