[Sailor Steve]

Dealing strictly with the Sino-Japanese war: the Chinese bought planes from anywhere they could get them, including American companies. They also hired mercenary pilots from wherever they could, and many of those were also Americans.

The same is true of the Republican side in the Spanish Civil War. American companies sold planes to whomever they could, and pilots flew for whoever paid the most, or whomever they liked. Doesn't mean the government was involved, even indirectly.

Of course it doesn't mean they weren't, either.