[Ruy Horta]

Japan was never forced to attacking US assets.

They might have gone south, without attacking any US assets, directly towards the NethEI, to capture the oil resources they needed.

Problem however would remain on their flanks, roughly: British in the West and South, Americans in the North and East.

Second option would have been an attack on both British and Dutch, but still bypassing the Americans.

Certainly this would have had a significant impact on American resolve to curb the Japanese, the case would have been far less personal.

Could the war have been more effectively waged if America had been drawn in more gradually? I think so, at least the chances of facing the old pacific fleet in a true naval engagement the Japanese craved for would have been more likely.

OTOH, during the whole early campaign the Japanese had to stretch their forces to the limit, all by a strict time table. Having a wild card US fleet on the loose would have seriously effected their operational freedom.

Would the US have entered hostilities at some stage, almost certainly, but that's another matter.