America forced Japan to open. It facilitated the modernization of Japan. 

She became an imperialistic country. Korea became a colony of Japan.

Then she conquered Manchuria and started the war against China. 

But people do not know Europeans and America funded the war

and supplied weapons to Japan. In addition, Japan could buy anything she needed for the war.

Invasion of Indochina where European colonies were turned around everything.

Europeans and the Japanese became enemies.

Americans sided with Europeans. Japan attacked America by bombing Pearl habor. Pacific war started. 

Would America allow Japan to have nuclear weapons on her own?

Historically, Japanese hates foreign interference as you appreciate it in the Japanese drama “사카모토 료마”.

Abe hates America contrary to his appearance. America knows it better than any other country.

In my opinion, the U.S. will not let South Korea and Japan have their own nuclear weapons.

Japan already has American nuclear weapons in Japan.

South Korea had them before and I wonder if the U.S. would redeploy them even though

there are plenty of NK in nearby Japan, not to mention nuclear submarines.

Nuclear proliferation in northeast Asia will make the U.S. hard to control nuclear nation going on their own. 

For example, the U.S. has to keep SK from inclining toward China.

It is much easier when SK depending on US nuclear weapons than her own. 

https://mnews.joins.com/article/23580063?cloc=joongang-home-newslistright

(중알일보: “대동아전쟁” - 금기어로 건배사한 아소 다로)

일본을 점령한 미국은 일본이 대동아 전쟁이라는 말을 쓰지말라고했다. 대동아 전쟁은 

일본이 아시아의 맹주가 되어 서양의 침략을 막자는 자비(?)로운 취지이다. 

https://mnews.joins.com/article/23580618?cloc=joongang-home-newslistleft

(중앙일보: 고노 다로 일 방위상 한국국방장관 회담 희망....소통할것)

Japan and South Korea have to sleep in the same bed because they have a common 

enemy, North Korea. In addition, U.S. is looking over them.

https://mnews.joins.com/article/23580750?cloc=joongang-home-newslistleft

(중앙일보 단독: 북한 일과 비밀 합의)

Japan knows the economic values of Manchuria and Siberia better than any other

country because she had been there. North Korea is on the way there. South Korea has to work closely with NK,  

China and Russia to minimize Japanese influence on the regional economy. 

일본은 왜 전쟁에 대한 죄의식이 없을 까?

Because they are "왜놈들". They are small people and will remain the same.