With a POD before 1854, keep Japan much weaker than China and its neighbors in terms of military and industry.
If Japan's in constant civil war then that will naturally increase industrial and military capabilities of the Islands so that the Daimyo will actually be powerful enough to take on nations. You can observe this in Sengoku era with the introduction of guns to Japan in a limited quantity and they quickly were being produced more in Japan than most other countries and the quality of the weapon was better than most nations as well. Japan had modernized before the Shogunate de-modernized it. Keeping Japan weak means keeping it isolated, to do that you need unity.Never have Japan unified and the emperor restored to power.
If that happened it would be a russia expanding into china, korea and japan...