Fun fact: Chinese Chess does have a river in the middle
On the other hand, Japenese chess is a full blown navy battel.
Is that so? I play shogi and I don’t understand what you mean. Or is the joke that Japan is an island?
One explanation I have read online is that its inspiration was navy battles and therefore you can use the captured pieces. Wikipedia states a possible connection to mercenaries and switching loyalties. Both seem reasonable enough.
I always assumed that the dropping of pieces was an influence of Go which wouldn’t explain the switching loyalties. Still your explanations don’t explain the change in position so it could be a combination of many influences or none of the above, who knows
new dota update going everywhere, pieces move downstream 2 squares where they would move one.