I understand they were trying to emulate Taranto with Pearl Harbor, so this is not an argument about that- but Germany went to great lengths to not get into a two front war. Japan had far less men (less than Germany, despite having a similar population) and much less industrial capacity. Why would they go for a two front war against two world powers at once and not simply increase efforts against China or even if they were to go for a first strike why not against the UK?
Was the US that close to joining the war before Pearl Harbor that they decided it was necessary to attack first? Would the US have joined the war if Japan did start an invasion into India/Burma or put even more pressure into China? Or perhaps they could have tried invading the Soviet Far East?
I do understand the IJA was having a lot of difficulties in China but as I understand it, the UK genuinely feared the Indian mainland being invaded (especially after Japan destroyed much of the English Navy in Indian Ocean and South East Asia). Now, I assume, it was just that hard for Japan to get their fleets around Singapore without the UK noticing? But if that's the case why not attack Singapore and Australia then? Malaya was not very well protected and neither was Australia.
And I guess the important question is, how would Japan fared in these cases? My knowledge of the Sino-Japanese war in its later stages (particularly from 1940-1945 is almost nil I hear almost nothing about it) but from what I understand neither Japan nor China could necessarily win due to lack of resources. But given Japan's success during the opening months against American and British forces I wonder how it would of fared if the Americans were missing. I guess the same could have been said about the Soviets if they decided to head north but I honestly don't know how well garrisoned and manned the Far East was. But I assume if Japan tried cutting the USSR from American supplies from the trans Siberian railroad and the British supplies through Iran would have helped Germany out immensely.
Short answer: Resources.
Long answer: an overly elaborate and foolish plan to grab Indonesia and the Philippines.
Japan's war in China had been raging since 1937, and their successes were largely predicated on two things: good discipline and good supply lines. When I say discipline, I mean the average Japanese fighting formation was generally better trained and held up better under pressure than the often haphazard arrangements of Chinese Nationalist or Communist troops. However, much of China at the time was internally undeveloped by the standards of the day, a consequence of almost 100 years of civil war, internal unrest, and government impotency. This meant that railways existed between major cities, but largely failed to reach into the countryside. It is an old adage that an occupying army only controls the country as far as their eyes and ears can reach, so the Japanese came to rely heavily on trucks, tanks, and occasionally aircraft to support their foot patrols in and around Chinese cities.
Enter the United States. As a relic of a few of the Unequal Treaties forced on China at the end of the 19th and beginning of the 20th Centuries, the United States Navy maintained a riverine naval presence in the Chinese interior to protect American citizens who insisted on doing business or conducting missionary activities far upriver of the Chinese coast. Most people know of these riverboats through the Steve McQueen movie The Sand Pebbles, and in the intervening time between the setting of that movie and the beginning of the Second Sino-Japanese War in 1937 their function had not changed greatly. In December, 1937, a Japanese air patrol came across the USS Panay, a riverboat traveling up the Yangtze River to Nanking to rescue American citizens from the impending fall of the city to Japanese forces. The patrol dove and fired upon the Panay, sinking it and killing eight people aboard. Though the Japanese government paid a multi-million dollar indemnity to the U.S. Government and formally apologized, alleging that the pilots had not seen the prominently displayed American flags on the riverboat, subsequent investigation of Japanese radio traffic suggested the Japanese patrol had been under orders to sink the Panay and had been actively seeking her out prior to the attack. The Panay never reached its destination, and the fall of the city the next day initiated the Rape of Nanking.
As evidence of Japanese atrocities in China grew over the next three years, the Roosevelt Administration was pressured to employ sanctions against Japan by the powerful China lobby and multiple human rights groups. The final straw came in September, 1940, when the Japanese Army - prompted by French inability to stop them after Hitler's stunning conquest of that nation in June of that same year and by fears that Nationalist China could use the railway link from Haiphong, Vietnam, to Kunming, China to import weapons and materiel - invaded French Indochina. In response, the Roosevelt Administration signed an embargo of American metal and oils to Japan, slashing Japan's imports of the former by more than three-quarters and squeezing the latter into near-nonexistence. Given that Japan is a naval nation, surrounded entirely by water, continued pursuance of the war in China and maintenance of the Japanese Empire required extensive naval operations; the American embargo placed the Imperial Japanese Navy in a position where they had less than 21 months of fuel stocks remaining and no hope of importing additional supplies under the new circumstances. Additionally, the Army in China was worried about being reduced solely to marching, a scenario that would have compromised both their air support and ability to move heavy artillery to the front. A plan, simple in its conception but complicated in its execution, was hatched.
The largest stocks of oil in East Asia at the time were in the Dutch East Indies - modern Indonesia. But given growing American opposition to the Japanese that had begun with the attack on the Panay, the Japanese High Command expected a decisive American military response to any invasion of the Dutch Indies. This was not necessarily illogical - if sanctions fail to stop aggression, military opposition remains a nation's only option in most cases - but the Japanese compounded the chances of American intervention by expanding their ambitions to include the Philippines as well, an American colony in 1941 and the home base of General MacArthur and tens of thousands of U.S. and Philippine soldiers. To neutralize the American forces in the Philippines as well as to have a decent shot at grabbing the oil of the Dutch East Indies, the Japanese Admiralty decided to make a gamble: they wagered that if the American Pacific Fleet were destroyed, and the Philippines and Dutch East Indies fell quickly afterward, the American public would be so stunned and the American government so unable to react that Japanese possession of these lands would be a fait accompli, and that the Americans would cut their losses and sue for peace.
Obviously Japan, to borrow a phrase, "misunderestimated" how the United States would react.
tl;dr: Japan needed resources to keep fighting in China. Maybe the invasions that you were talking about were in the cards (Burma certainly happened by 1942, at any rate), but with the American embargo in 1940 Japan simply could not fight a modern, oil-based war for very long. In order to continue these wars, Japan needed oil - something they could only get from the Dutch East Indies. Anticipating American naval intervention in either case, the Japanese hoped that destroying the U.S. Pacific Fleet would leave Washington with no choice but to make peace.
It's worth looking at the ideological construct that Japan embraced to justify the war - the idea of a Greater East Asia Co-prosperity Sphere. This concept called for a unified Asian nation with Japan as it's nucleus. Japan committed to use force to free Asian territories from western oppression. This included American territories - Philippians, Wake and Hawaii. (Source: http://www.amazon.com/Winstons-War-Churchill-1940-1945-Vintage/dp/0307388719)
The Japanese felt that the United States - despite a long tradition of anti-imperialism and open hostility to the British Empire - would come to the UK's aid if Japan went after any UK dominions. (Source: http://www.amazon.com/Japan-1941-Countdown-Eri-Hotta/dp/0307594017) In fact, Churchill several times was deeply apprehensive about the possibility that Japan would only strike the UK, and that the United States would not involve itself in the war (Source: http://www.amazon.com/Winstons-War-Churchill-1940-1945-Vintage/dp/0307388719). Japan's "Southern Operations" were therefore dependent on eliminating the two rival powers - the UK and the US.
The attack on Pearl Harbor was just a part of the story. The Japanese had operations targeting India, New Zealand, China, Hawaii, the Aleutians. Therefore even though elements of the Japanese Navy wanted to immediately follow up on Pearl Harbor with a invasion (source: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0CFQQFjAE&url=http%3A%2F%2Fwww.usnwc.edu%2Fgetattachment%2F59d3fa3c-3a53-49f6-9f28-6f0358389db8%2F-Winning--the-Pacific-War--The-Masterful-Strategy-.aspx&ei=8noqU_yZDMiGogTazYDYDA&usg=AFQjCNHOY-tYSJMeyFOL54nw44u5OfmcSw&sig2=Sn-sibfChG7xKQlpf2pEww&bvm=bv.63316862,d.cGU) They simply did not have the manpower to pull off everything they were trying to do.
Did the Japanese thinking about making a quick peace with China or Britain the way they were able to with the Soviets?
Was it anywhere near feasible to consolidate their gains?