What the Qing wanted from Japan at the time (i.e., the end of the 17th century) was silver and especially copper. While the amount of these that they were able to import was less than they wanted, it was enough to meet the most urgent demand. Japan was not a threat - they had sold weapons and sulphur to the Ming loyalists on Taiwan and the Three Feudatories rebels, but with the defeat of the Three Feudatories Revolt and the conquest of Taiwan, Japan could no longer support anti-Qing forces.

What benefit would there be from invading Japan? The Qing had been content to leave Korea independent after their two invasions. Their first invasion of Korea forced Korea to resume cross-border trade with Manchuria and cut direct military aid to the Ming, and the second invasion restored this state of affairs after they had broken down, and also made Korea a Qing tributary. The Qing had bigger ambitions (the conquest of China) and had what they wanted, and Korea stayed independent. After the Qing conquest of China, with Korea a reliable enough tributary and trading partner, what would be the benefit of conquering Korea? The question to ask about Japan is essentially the same: what would be the benefit of invading Japan? The Qing were getting silver and copper, which they wanted, and an unsuccessful invasion would cut this off. Given that Japan had put two armies in excess of 100,000 men into Korea a century earlier, it was clear that Japan would be no pushover. Perhaps an invasion would succeed, but (a) it would be very, very expensive, and (b) it would, at least in the short term, cause a serious copper shortage.

Besides, the Qing had distractions. With the fighting in the south recently over (the Three Feudatories Revolt), it was time to try to get the economy to recover, and rebuild the treasury. Russia was a dangerous neighbour, and there was an ongoing war with Russia over the Amur region. This was resolved with the Treaty of Nerchinsk of 1689. By this time, the Qing was at war with the Dzungar Mongols. The Dzungar-Qing wars lasted past the end of the Kangxi Emperor's reign, through his successor Yongzheng's reign, and was finally ended by the next emperor, Qianlong. This victory brought Xinjiang under Qing control. In the midst of this was fighting with the Dzungars over the control of Tibet, also brought under Qing control. Qing expansion - not entirely planned - was inland, to the west.

Qianlong proceeded to fight wars with Burma, with Nepal, and to launch a military intervention in Vietnamese politics. The White Lotus Rebellion, lasting past the end of the 18th century, was yet another distraction.

With all that going on, would invading Japan appear an attractive prospect?

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!