What was the cause of WWII in the Pacific?
The immediate cause was the Japanese attack on Pearl Harbour in December 1941.
Although this was the catalyst for war, there were also long term causes. The militarism which dominated Japan in the 1930's called for and instigated a brutal, expansionist foreign policy.
The Japanese had already occupied Manchuria and other areas of China imposing a regime which was notoriously violent ( The Rape of Nanking.)
This expansionist militarism meant that Japan needed access to raw materials to sustain a war economy. This would not only bring her into conflict with colonial powers such as Britain, France and Holland but also the USA.
The Japanese attack on Pearl Harbour was a pre-emptive strike aimed at destoroying the US fleet in the Pacific and forcing the USA to sue for peace.
It failed and it could be argued that as early as this Japan's defeat was assured.