“There is a reason why Austria-Hungary, Britain, France, Russia, Italy, Britain. America and Japan all allied against them.”
Yeah, to gain territory for their empires.
“Whatever China’s grievances (some clearly legit), just murdering every foreigner they could get their hands on was barbaric, unjust and quite stupid.”
What would you do if the African, Arab, Chinese and Mexican invasion here progressed to the point that those foreign nations began to carve up and administer the USA and demanded the US government enforce their edicts?
I’d plot, and kill everyone of them I could.
If you just kill every foreigner innocent or guilty, combatants or non-combatants, don’t be surprised when everybody gangs up against you.