Is there a viable "Japan First" strategy for the Allies in Axis and Allies?
This response for Japan First is based on the 1986 Second Edition version and assumes No Russia Attack first round house rule.


The allies should under no circumstance look to divert SIGNIFICANT RESOURCES (i.e. more than U.K.'s dollars to an India IC/tanks thereafter).
If you send more dollars (U.S. IC, Russia support, etc), you are weakening the Shuck-Shuck which ultimately means a delay to round 4 assuming a smart Axis German player will suicide his fighters on a weakened initial shuck-shuck attempt. ORRR you are needlessly increasing Germany's short initial window to attack Russia by not placing all Russia defense troops possible of reaching Karelia as defense.
Allies should concentrate their initial 90 IPCs as much as possible towards Germany's 32 IPC's, this tilts the ground war in their favor the quickest as Germany starts out with an IPC advantage day 1 which must be overcome via Infantry-push tactics.