I'm a bit late to the party, but I feel the need to respond to this: "Has Japan ever put Americans in concentration camps?"
First, I should point out that internment camps are different from concentration camps. While the American (and Canadian) governments might have rounded up the Japanese and forced them into camps, they were not systematically exterminated, nor were the people there subject to biological experimentation. The Japanese, on the other hand . . .
http://en.wikipedia.org/wiki/Unit_731
Some excerpts:
"Between 3,000 and 12,000 men, women, and children[1][2]—from which around 600 every year were provided by the Kempeitai[3]—died during the human experimentation conducted by Unit 731 at the camp based in Pingfang alone, which does not include victims from other medical experimentation sites.[4] Almost 70% of the victims who died in the Pingfang camp were Chinese, including both civilian and military.[5] Close to 30% of the victims were Russian.[6] Some others were South East Asians and Pacific Islanders, at the time colonies of the Empire of Japan, and a small number of Allied prisoners of war.[7] The unit received generous support from the Japanese government up to the end of the war in 1945."
"Prisoners, including one known POW,[15] were subjected to vivisection without anesthesia.[16] Vivisections were performed on prisoners after infecting them with various diseases. Researchers performed invasive surgery on prisoners, removing organs to study the effects of disease on the human body. These were conducted while the patients were alive because it was feared that the decomposition process would affect the results.[17] The infected and vivisected prisoners included men, women, children, and infants.[18]"
Another article: http://en.wikipedia.org/wiki/Japanese_war_crimes
More excerpts:
"One case of human experimentation occurred in Japan itself. At least nine out of 11 crew members survived the crash of a U.S. Army Air Forces B-29 bomber on Kyūshū, on May 5, 1945. (This plane was Lt. Marvin Watkins' crew of the 29th Bomb Group of the 6th Bomb Squadron.[78]) The bomber's commander was separated from his crew and sent to Tokyo for interrogation, while the other survivors were taken to the anatomy department of Kyushu University, at Fukuoka, where they were subjected to vivisection or killed.[79][80]"
"Many written reports and testimonies collected by the Australian War Crimes Section of the Tokyo tribunal, and investigated by prosecutor William Webb (the future Judge-in-Chief), indicate that Japanese personnel in many parts of Asia and the Pacific committed acts of cannibalism against Allied prisoners of war. In many cases this was inspired by ever-increasing Allied attacks on Japanese supply lines, and the death and illness of Japanese personnel as a result of hunger. According to historian Yuki Tanaka: "cannibalism was often a systematic activity conducted by whole squads and under the command of officers".[110] This frequently involved murder for the purpose of securing bodies. For example, an Indian POW, Havildar Changdi Ram, testified that: "[on November 12, 1944] the Kempeitai beheaded [an Allied] pilot. I saw this from behind a tree and watched some of the Japanese cut flesh from his arms, legs, hips, buttocks and carry it off to their quarters ... They cut it [into] small pieces and fried it."[111]"
I haven't read anything about systematic targeting of groups, ethnic or otherwise, so I guess it's fair to say that the Japanese didn't have concentration camps as we understand them. However, a comparison of the respective wartime actions of the Japanese and the Americans (or most of the other countries engaged in the war) shows us that, while interment camps were bad, the Japanese were worse.
I gather from your initial post that you are becoming a weeaboo. Stop.
As others have pointed out, Japan has numerous problems that aren't exactly the same as American ones. I think you'll find that Sweden is a better country to compare the USA to if you are looking to score points from the "left". (I use "left" in quotation marks because there are no mainstream leftists in the USA; indeed, the left is dead in North America).