From my knowledge, the high level contours of Japan's imperial ambitions in the early 20th century were to secure resources for the metropole and create buffers between themselves and European powers. But when I read up on the prelude to the Second Sino-Japanese war, I see a chain of incidents and I don't see how they all connect.
Mainly, what did they actually want, in the long term, from China? What was the goal? Did they seek to annex portions of the country? Install a friendly government? Was it a coherent plan, as it sometimes seems like the IJA is just winging the war as they go along. And, had they won, did they think they could control a massive China given their relative population size? Was the military and political leadership thinking that far ahead?
I'm not asking for a counterfactual--I'm interested in what members of the Japanese government and intellectuals viewed as feasible goals, and if that changed as the Second Sino-Japanese war blurred into WWII.
But when I read up on the prelude to the Second Sino-Japanese war, I see a chain of incidents and I don't see how they all connect.
Ding ding ding! This was the Japanese side in a nutshell.
Japan's imperialism ultimately only really boiled down to one simple concept. Don't get imperialized by the Western Powers. Everything else was secondary compared to this goal.
In the 1800s and early 1900s, Japanese foreign policy was conducted entirely in this manner. First, there was a massive propaganda offensive to make Japanese institutions seem as similar to those of the West as possible. This stretched from large numbers of foreign students being sent to Europe and the US, to Japanese scholars talking about the similarities between medieval Chivalry and Japanese samurai Bushido (which arguably wasn't really a thing until this point), to the eventual conquest of Korea and Formosa/Taiwan (where for a good 20-30 years, colonial policy was essentially to make it as cheap to maintain as possible). As far as Japan was concerned, the appearance of being a great Western power was much more important than deriving any real benefit from their policy. They figured that by convincing the rest of the world that they were Europeanesque, nobody would attempt to invade them or take trade concessions like they had in other parts of Asia. And to a large extent, it worked!
After World War I, this Europhilia slowly gave way to a rising anti-Westernization in the military as tensions rose with the once friendly United Kingdom and the United States. It was at this point that Japanese foreign policy began to change shape, from being a willing participant of the world to carving out their own hegemony in the world, similar to how the UK appeared to carve one out in India and the US in the Americas. China, being still decentralized and split between rival warlords, was naturally an obvious target of this policy, as was Malaya and the Dutch East Indies.
The thing was, the Japanese government was fully aware of the fallacies of launching a direct invasion of China. Aside from the numerous European interests and concessions there, to say nothing of substantial American interests, the Japanese military was simply not built to fight an extended war, the likes of which would almost assuredly be fought in China. It was a military designed to fight in decisive engagements and pitched battle, not a grueling mudslogging campaign far away from logistical centers. It was much easier to simply pursue diplomatic goals (like the attempted 21 Demands), economic interests and take over railways and the like over time.
Unfortunately, not all members of the Japanese military thought like this. Some particularly hotheaded members of the Kwantung Army proceeded to launch a unilateral invasion of China without permission from their superiors or the government, and succeeded in capturing most of Manchuria before they could react. Government attempts to take control of the situation were stymied by a wave of popular support for the hothead officers (which was in all likelihood due to government efforts to whip up race tensions between the Japanese and the Chinese). So the government had no real choice but to accept the fait accompli perpetuated by these officers, which in turn antagonized China (and much of the rest of the world)... and more or less began Japan's stumble towards war. Ironically, one of the hot headed officers in question, Kanji Ishiwara, later became head of the army, where he was most notable for personally flying to China to head off a full scale conflict after another hothead officer invaded Northern China (he failed, starting the war proper), and then denouncing Hideki Tojo for much of the rest of the war.
In other words, the Japanese really didn't have any solid idea what they wanted to do with China. This applied from both the political perspective (conflicts between the collaborationist government and the military that effectively turned significant areas into its personal fiefdom) and the military perspective (many Japanese defeats resulted from uncoordinated attacks by glory-seeking commanders, and Japanese strategy in forcing a Chinese surrender shifted constantly as their expectations failed to be fulfilled. Ideally, the government just wanted a victory of some sort. If they came back with any less, they faced popular discontent at home and with the military (that they had little control over) and the Japanese military simply could not achieve victory given its logistical constraints. It was these sorts of considerations that led Japan to consider the suicidal option of going to war with the Dutch, UK, and US... and we all know how that ended.
As an afternote, it's also important to understand the Soviet communist threat to the Japanese. The Japanese were deathly afraid of communism and especially of its spread to China. Part of the reason for their invasion was allegedly to stamp out communism in China: however, most of the fighting was against Chiang Kai-Shek's nationalists, so make of that what you will.