One should look a little more closely at Japanese history from 1894 onwards. Staring with a war with China in 1894, the Japanese invaded Formosa, the Sahkhalin Islands, Korea, Manchuria and then as much of China that they could grab. Their long-term intention was to build a far-eastern empire which would include ultimately the Philippines, Indonesia, French Indochina, Thailand, Malaya, Papua New Guinea, the Pacific Islands and Burma for the resources and strategic bases that these countries offered. This was not a flash-in-the-pan following Pearl Harbour; it was a long-term imperial strategy. During the course of the Japanese reign 19 million Chinese were murdered, 2 million Vietnamese were starved to death when the Japanese seized a year's entire rice crop and a large number of others eleswhere were killed. During this time as many as 250 000 "comfort women " or more from the conquered regions were forced into prostitution, as were a considerable number of Japanese women brought from Japan to the conquered territories for the pleasure and profit of the Japanese occupation forces. The Japanese occupation forces in Manchuria, Korea and China were also deliberately pumping narcotics into these conquered areas as deliberate policy to create revenue for Japan. The occupation forces also practised large-scale terrorism and kidnapping of Russian refugees in Harbin and other places as well as wealthy Chinese and Koreans so as to hold them to ransom for large sums of money that were paid to the Japanese occupation forces.
This is all documented, although the Japanese refuse to accept these facts in their education system.
Seen in this light the USA's embargo of Japan was fully justified and was no provocation.
As for dropping the two atom bombs on Japan. All bombing of civilians is a war crime, although one could argue, as did "Bomber" Harris, that killing workers in factories producing war materials is fully justitifed.
It would appear that the reason for dropping the two atomic bombs on Japan was more to dissuade the USSR, which had declared war against Japan around 10 days previously and was recovering the Sakhalin Islands, than it was a military necessity to force the surrender of a nation that by 1945 was completely wrecked as a military entity and within which the civilian infrastructure had been seriously damaged.