Japan's invasion of China was quite successful. Please quantify "success". They certainly took and held territory that was valuable, but at the same time they were also tying up an unreal amount of resources and man power holding that territory. Contrary to what the Chinese government likes to say today the Japanese didn't just walk all over China who was then on the receiving end up defeat after defeat after disaster after disaster.

Japan was in the midst of modernizing. They had been for years. The US had a keen interest in opening Japan to trade in the 19th century, but due to their isolationist policy had very little success- largely only a set of engagements done at the behest of the Dutch, flying Dutch flags in situations where they logistically could not carry out trade missions- it wasn't till 1849 that the US captain James Glynn went to Nagasaki and was met with some success. He then recommended that Japan needed a demonstration of force to make them properly pliable to US negotiations. Four years later in 1853 Commodore Perry would park a few ironclads in Tokyo (Edo at this point) Bay (to be precise, the Shogunate had told him to go to Nagasaki, he ignored the order and simply piloted his ships to Tokyo) , threatened aggressive action if Japanese vessels did not disperse from the US vessels, gave the Japanese a white flag for them to use should they try to respond in force, then ordered a few buildings in the harbor be shelled- important because the guns his ships were equipped with were Paixhans guns, some of the first to employ high explosive rounds- to further illustrate his point.

Such actions highlight the fact that Japan could no longer remain a blindly closed country. Yet at the same time Japan was actually pretty poor. Between a virtually absent manufacturing sector and a lack of any real resource riches- poor quality iron which required something between magic and witchcraft to turn into anything useful, coal which was available from many other sources, and little else- Japan found itself much in the same situation the Russian Empire found itself it- modernizing would come, but it'd come at a great cost to the citizenry. I think it was the Finance Minister Sergei Witte in Russia who said that if the country had to choose between spending it's gold to import the means to industrialize, or the means to feed it's people, it was going to have to let it's people starve. Such was the paradox- to remain autonomous and free from European and American colonization, Japan had to import materials, designs and knowledge from the US and Europe.

If you're looking for the ballistic figures you see for the rate of modernization in the US in the late 19th / early 20th century, and a little later for the Soviet Union in Japan, it's not quite there, but they were still doing it at a break-neck pace. Unlike, say, the US, Japan had to be far more reliant in it's import economy to modernize. They simply couldn't make something like aluminum, they simply had no domestic oil, and their means to producing steel would never really reach figures that were remarkable- the competition for the resources necessary to produce war machinery in WW2 for Japan was notorious between the Navy and the Army.

In this sense, yes, Japan was absolutely doing it more effectively than China, but then Japan didn't have nearly the sovereignty issue China wrestled with in this period- while Japan may have been open to trade it was extremely distrustful of outsiders. Prior to the 20th century there was more than one rebellion that had to be put down, the Boshin war being the bloodiest of them.

The particulars of why Japan become so militaristic in the 20's and 30's isn't something I'm actually very well read in either, but I answered your follow-up questions.