zhukov44. you pose an interesting question. With the standard buy of 3 transport 1 inf… you could woop him if he moves to amur on J2… this would require your air forces to be out of range, it would broadcast to the allies you may not be war ready come J2 (which means russia could just end up hanging back).
I do not like killing worthless russian inf when I could cut into worthwhile uk pacific income. The capital that needs to be taken is calcutta. In order to achieve victory in the pacific, calcutta is necessary. Most Japan players will lean toward min/maxing their efforts for that objective and for the NO of the dutch islands.
The income you lose from korea is only 3 ipc a turn. Manchuria is another 3, but he can no longer get mongolians on his side and generally speaking your naval is in range and so are some infantry.
Also korea is not a victory city. After india… south whales or hawaii is what you need… anzac is right after india so all the fighting should occur down there… still 60+ buck japan without korea or manchuria.
This is why J2 is generally the round you drop an airbase and your minor ICs. J3 is the round USA 1 units are generally where they need to be in threatening your islands… J3 is when the buys diverge on case by case analysis.
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also check out my japan playbook it is where i post standard openers