jobs like these provided a finacial support system that cold support many people and even if oyu didnt have land to be in agriculture you could still make a living
The best and correct answer would be It was in an area of the world that emperors did not want to conquer. This is a strong country with brave emperors which the other countries do not want to deal with.
They wanted to secure islands in the pacific because they needed a ground to stand on and then they could invade Japan a little bit easier because then they could ship supplies easier therefore getting it done quicker.