The US government and occupational forces have not created a RKBA in most places they have designed the government.
Japan is a major one as you mention.
Another one is South Korea, where only the police and military are suitable.
The same goes for the US backed Transitional Federal Government in Somalia.
A unique example seems to be Iraq, where the citizen is permitted to have an AK (no handguns, or other types of weapons, and even fine crafted expensive double shotguns have been confiscated.)
The US government has long been the primary influence in NATO, and of the UN, and the UN actively works to disarm the citizens of the world.
Treaties and trade restrictions are established, and even laws on export effecting US citizens stem from such pressure.
The US was the primary force of Western Germany before the fall of the Berlin wall. Do you think West Germans had firearm rights?
The American government attempted to disarm the Philippines through government and legislation, though the people have resisted it.
The US government has long had a large influence in politics in the Western Hemisphere, yet many of the nations it has had the biggest influence on in South and Central America are anti gun.
Then you have US territories past and present, almost all of which were denied the RKBA even though the US was the effective controller of the nations.
American Samoa, Guam, Marshall Islands, Federated States of Micronesia, Northern Mariana Islands, Palau, Puerto Rico, and the Virgin Islands (U.S.) are all generaly anti RKBA.
Pretty much most places the US has had a significant role in establishing or maintaining the government, or the primary influence, the US has not extended the 2nd or the Right to Keep and Bear Arms.
Yet the US citizens have not demanded this of thier government either.
So yes if the government could create a new government in the United States I imagine the RKBA would not be included. Leaders of nations usualy do not want thier subjects armed, that should come as no surprise. Those few permitted arms they want to insure are possessed by those who go through a process that includes strict background checks and only favors certain content successful people, not the rabble likely to use them for non sporting purposes.
The founding fathers recognized this tendency, and knew it was the natural direction of government. That is why it "Shall not be infringed" *
* Except in every single possible way deemed reasonable, and inluding all prohibited classes henceforth created.