It seems completely absurd to me to blame the Chinese for fentanyl use in the US. Comparing it to the opium war is even more ludicrous.
Where there is a black market, criminals (of any nationality) will step in to fill the void.
If you want someone to blame, I'd suggest looking a lot closer to home: pharmaceutical companies made false claims about the addictiveness of their opioid drugs, as well as about the duration of effect of their extended release variants; many US doctors and dentists were prescribing large quantities of opioids where paracetamol/ibuprofen would have been more suitable; and of course there is decades of futile and harmful US drug policy.