In the early 1850's, the United States was trying to open up Japan to the outside world. When Mathew Perry first arrived in Japan he delivered an Ultimatum, sign a treaty opening up to the west for trade, or be attacked.
My POD is that Japan refuses to open up, forcing Perry to attack Japan when he returned from china with an even bigger fleet. Did America have the capabillity in the 1850's to acquire and hold a colony in the far east? Could America have Imperialised Japan in the !850's?
I have another Idea for this scenario. In OTL China resisted Modernization, and Japan embraced it. What if this was reversed? China imbraces Westernization, and Japan resists. This leads to Japan being imperialized, and China becomes the eastern Juggernaut.
How plausible is this scenario. What might need to happen before hand to make it possible.