[Rich47]

An initial attack into Manchuria didn't make any sense for the Japanese. They knew their main adversaries would end up being the Americans and the Brits anyways, "also knew they would end up being at war with them eventually", so why tie up your forces in Manchuria?

There is some argument for Manchuria being "resource rich" but it was second in importance to the oil rich British colonies in S/E Asia. Doubly so after the American oil embargo!

Besides Japan was 100% dependant on imports for its war industry. To leave their extended sea lanes vulnerable to the powerfull Brit and American navys would have been madness. The Japs had two options open to them in 1941. #1, Was to give up their dreams of empire. #2, Was to attack the American Pacific fleet, hopefully crippling it enough for them to get a few years to shore up their Empire, eventually getting a peace on their terms. Manchuria was on the short list but it wasn't a main objective.