How does this justifies, or even slightly downplays what they did in ww2?
It justifies what the Japanese did in China or had to do in China because Japanese had not been aware of how to behave with the surviving enemies one has defeated. They were not aware of the conspiracy of European colonizers who used the Japanese as cannon fodders in China, asked them to be photographed while committing atrocities and then used those photographs to spread anti Japanese propaganda through missionaries and evangelicals in China, so that entire blame goes to the Japanese.
Japanese did realize that In 1919 when Japan submitted its Racial Equality Proposal in the League of Nations but was refused by the Americans who didn't consider East Asians as human beings at all and so no question of racial equality. Japan realized where it had already gone wrong. But it was too late to do anything.
During the Opium Wars, watching the Chinese misery in the hands of Western White colonizers, Japan had first realized that the East Asians would soon be like no more than Native Red Indians and other tribes in the Americas. The first Opium War was brutal and Japan had rarely any access to what was happening in China. The heard reports of indiscriminate massacre of mass Chinese populations in the hands of Western invaders. There was no international media, no Television, no internet to monitor how the invading army is behaving in China. But during the second Opium War (1856–1860), Japan received first hand witness to the inhuman slaughter of innocent Chinese people by the Western white men. If you read the contemporary Japanese writers, you will know how much favorably the Japanese viewed the Chinese.
The end of 19th century opened Japan's eyes and made them realize that China would slowly become a history if they would not come to their rescue.
By the start of the 20th century, Japan decided to take first step, it engaged Russia in 1904-05 to stop it from eating up entire Manchurian region. The Russo Japanese war began and for the first time an Asian nation defeated a Western white nation. Japan was admired by all Asian nations for its victory and engaging a Western white nation for a just cause. In those days, racism was at the peak. White men obstinately felt themselves to be superior to the East Asians who they sometimes didn't regard as human beings!
In 1919, Japan submitted its Racial Equality Proposal in the League of Nations but was refused by the Americans who didn't consider East Asians as human beings at all and so no question of racial equality. Japan being pissed off, decided to end Western white colony at least in the neighboring regions.
"Ask a typical American how the United States got into World War II, and he will almost certainly tell you that the Japanese attacked Pearl Harbor and the Americans fought back. Ask him why the Japanese attacked Pearl Harbor, and he will probably need some time to gather his thoughts. He might say that the Japanese were aggressive militarists who wanted to take over the world, or at least the Asia-Pacific part of it. Ask him what the United States did to provoke the Japanese, and he will probably say that the Americans did nothing: we were just minding our own business when the crazy Japanese, completely without justification, mounted a sneak attack on us, catching us totally by surprise in Hawaii on December 7, 1941.
You can’t blame him much. For more than 60 years such beliefs have constituted the generally accepted view among Americans, the one taught in schools and depicted in movies—what “every schoolboy knows.” Unfortunately, this orthodox view is a tissue of misconceptions. Don’t bother to ask the typical American what U.S. economic warfare had to do with provoking the Japanese to mount their attack, because he won’t know. Indeed, he will have no idea what you are talking about."
In the 1940, at the sight of Japan trying to liberate China and southeast Asia from white Western colonizers, US imposed blockade and embargo to soften the target as US had already decided to invade Japan and remove the obstacle in its way to colonize the rest of East Asia.
The Hull Note served as the ultimatum to Japan by USA in 1941. It was a declaration of war against Japan before the Pearl Harbor attack. After declaring war against Japan, USA waited for Japan to react so that USA get the excuse for a full fledged invasion of the East Asian savior.
On November 25 Henry L. Stimson, United States Secretary of War noted in his diary that he had discussed with US President Franklin D. Roosevelt the severe likelihood that Japan was about to launch a surprise attack, and that the question had been "how we should maneuver them [the Japanese] into the position of firing the first shot without allowing too much danger to ourselves.'" Hull note - Wikipedia, the free encyclopedia
Japan made mistake by believing the Germans as invincible. In May 1945, after the fall of Berlin, Japan's last hope was shattered. Germans were the only ally Japan had been left with. USA bombed Tokyo and other cities to the stone age killing millions of innocent Japanese civilians. Japan knew they would have to sacrifice themselves for the rest of East Asians.
After three months since the fall of Berlin, Japan's Hiroshima was nuked on 6th August 1945, by USA.
USA had already learnt of the Russians making similar plans to invade and occupy Japan as they did in case of Germany. So USA made every effort to force Japan into submission so that entire Japan becomes a US colony, not giving a chance to the Russians to occupy Japanese lands. So USA started dropping nuclear bombs on Japanese mainland to scare off the Russians and force the Japanese to surrender as well.
Suddenly in early August Russians declared war against Japan and proceeded to invade Japan on 8th August, 1945. Japan had seen what the Russians did during the invasion of Berlin a few months ago. Meanwhile another nuclear bomb was dropped on Nagasaki by USA. Japan decided to surrender to the US with the hope that US soldiers would not rape Japanese women after landing on Japan. They heard that American forces behaved in a better way than the Russians in Germany.
However, they soon realized what they thought was wrong. US troops behaved better in Germany but worst in Japan raping all the women of Japan. Douglas MacArthur put censorship on news media so that American GIs could rape all the Japanese women in the first systematic ethnic cleansing the mankind has ever seen. Japanese were gone.