For one thing, holocaust denial and promotion of Nazism is illegal in Germany, so I'd say that they take their "bad" history pretty seriously.

But to answer your question about "the American war"...which war do you mean? Europeans and their descendants have been waging war with Native Americans pretty much since they got here. The United States of America has gone to war against the Seminoles, Cherokees, Creeks, Lakotas, Apaches, Navajos, Utes, Comanches, Cheyenne...the list goes on and on. Perhaps the various wars are portrayed as "bad" because frequently they explicitly broke treaties that were signed with Native Americans, such as the 1876 war against the Lakota and Cheyenne for the Black Hills. Several events reported by the American army as "battles" were actually massacres, like Wounded Knee, Sand Creek, Washita, and Bear River. The American army deported entire tribes to foreign areas, such as on the Trail of Tears and Navajo's Long Walk. It's difficult to discuss Native American history without coming across some type of atrocity.

It's also important to recognize that Native American history didn't end at Wounded Knee in 1890 - these communities and nations still exist today. The consequences of these wars are still being felt today - compare the 1868 Sioux reservation boundary with present tribal lands, and then consider that Pine Ridge (second source) is basically a third-world country.

However, I don't know that this history is any better or worse than, say, the Belgians in the Congo, or the British in India, the Turkish genocide of Armenians, or the Japanese in China and Korea in WWII. Generally speaking, though, it's not surprising you learn more about your own country than others.