@simon33:
Are you advocating unloading all CV and attacking Yunnan with everything? Hmm.
Japan can get in 11ftr 8tb 2sb and maybe 2inf vs 14inf (including 2UK units) and 1tb. On average, Japan loses 2inf 3ftr in the first round for killing 13inf. It needs to trade planes to take the territory.
Japan is in the position to trade a few planes to totally decimate the combine Chinese and British if they stack Yunnan for J2.
The longer you wait, the worse that stack becomes to dislodge. Not to mention, you now have to worry about your weaker flanks in China being exploited (FIC, Northern China)
As in betting in poker, once you raise after the flop you have to continue raising or you forfeit the lead (assumption you have the best hand). If you give up the lead, then everyone knows you don’t have the best hand and may start calling your bluff. Even if you don’t have the best hand, once you’ve committed, you better play like you do or you’re throwing money away.
Same theory applies for Japan. You take Yunnan every turn, forcing the predictability of both China and India in being forced to send forces to re-take it and defend it, or they must admit defeat - which means you’re gearing for Calcutta with all future purchases. Forcing your opposition into predictable moves is essential for Japanese success. The board is too big and there are too many flanks to allow someone else to dictate your moves.
The second you let China and India do anything else with their purchases, you’re giving up the “lead” and therefore conceding “defeat”. Defeat is defined as they’ve made you spend more time and resources to achieve an end you could have reached more rapidly and with less economic investment (starting units are sunk costs and are not economic investments).