Probably a little of the other countries, followed predominantly by China, and that the common denominator was unrestricted free trade with poorer countries. As the other countries liberalized and conditions for workers improved they became less valuable places to offshore production to. Mexico and especially China remain countries of cheap labor due to political conditions and thus the high deficits.
I think there's a better argument for trade at large, since ~1970 was a turning point for many _other_ Asian countries, in particular Japan, Taiwan, South Korea, Singapore, etc. There wasn't a clear, sharp line, though.
[1]https://static.seekingalpha.com/uploads/2018/2/15/saupload_c...