Is it really cheaper to mine coal in the US with (mostly) unionized miners, and ship it 6000 miles to China vs mining it in China with low paid serfs?
Yes, it is
Check the stats on US coal exports to China under Barky
Huge jump
Easier and cheaper for China to fuel its burgeoning coastal cities and industries with coal shipped from us than to upgrade logistics to get coal moved from chinese interior mines to its coast