From what I understand, the invasion of Korea in the late 1500s by Toyotomi Hideyoshi, the then de facto leader of Japan (and comparable to the devil according to a Korean friend of mine), launched an invasion of Korea with the aim of conquering it and using it as a stepping stone towards invading and conquering all of Ming China. Was this at anytime a realistic goal? I assume that Japan had the most skilled and most technologically advanced, if not the biggest, army in the area, through be sure to correct me if I am wrong about that. But even with an advantage in the quality of their armies, could the Japanese realistically compete with the sheer manpower of China at this time? If The Korean navy was not so successful would Toyotomi have actually stood a chance of success? Was it always a pipe dream? Were any of the higher ups of Japan at this time skeptical of the campaign's possible success? Please feel free correct me about anything in my question that I got wrong.
Toward the end of his life Hideyoshi become increasingly unbalanced.
He did actually said to some european visitor that after China he would have marched westward to Europe India (see the edit below); he obviously was not able to understand the distances involved and the size of the countries he did plan to conquer or cross.
Regarding the invasion of Korea: the korean navy victories were significant but not in itself sufficient to stop the japanese invasion; really the invasion ended when Hideyoshi died in 1598; the situation in Japan was highly unstable, Hideyoshi heir was a five years old, the council of regents was divided and the country in just two years slided back in civil war.
If Hideyoshi had died ten or fifteen years later (and kept his sanity ...), he would have certainly continued the Korean war, and would have quite probably been able to keep Japan united, and pass it whole to his heir. It is of course impossible to say if all this in the end would have made any difference for the success of the korean invasion.
My source for the above A History of Japan of George Sansom; when I will be able to check my copy I will try to report the exact quote about his plans after the conquest of Korea.
EDIT: OK, I have checked my books (A History of Japan by Sansom and Hideyoshi by Mary Elizabeth Berry) and I have not really found a reference to India; but there are multiple letters of Hideyoshi talking about his expansion plans in Asia.
In 1591 he wrote to the Portuguese Viceroy of the Indies, at the end he said that he was planning to subdue China shortly, and then he would be nearer to India so communication would be easier.
Also, "He said more than once that he would go on to Southeast Asia and India and Persia after conquering China" (Samson, page 378).