Here's what's my problem with this: Most history textbooks in school tend to make American history nothing but negative after negative: Imperialistic White men killing indians, Revolution, Rich slave owning wig wearing White men write a constitution that is now outmoded, Slavery, Civil War, Greedy businessmen crushing the poor Government and Unions save the poor, WWI, Roaring Twenties, Great Depression and FDR and the New Deal saves the country, WWII and the Japanese internment camps, the red scare paranoia(McCarthyism), Then the country was saved by the New Left Movement and the hippies were just expressing themselves (Just like Crazy Charley Manson), Vietnam, Nixon and Watergate, and the Fascist Warmongering Idiot Reagan, Clinton, Stupid Warmongering Bush, and finally the greatest president of timeOBAMA. So you can understand I don't like it when a group of revisionists attack the worst attack on American soil (before 9/11) and insulting military. Also it seems that the people that do these Textbooks agrees with them. Also they want to turn the Arizona Memorial in to a memorial for both Japanese and American deaths. Now remember this is the country that now Santa Claus can't say Ho Ho Ho because it's not Politically Correct. So...
I teach history with actual American history textbooks. What you are saying is simply not true.
We have several official state-authorized textbooks. On the whole, they give a round, objective presentation of major events of American history. When Americans have done bad things, they present the facts; when Americans have done great things, they present the facts.
To the extent there is any bias, I've found from looking at a variety of textbooks, that unpleasant events tend to be omitted (for instance there's no mention of military atrocities against Filipino civilian populations in the Philippine Insurrection at the turn of the century, nor any mention of municipal government complicity in the bootlegging operations run by the Mafia during Prohibition).
I have to wonder where you got the entirely inaccurate idea that US History textbooks focus on "nothing but negative" parts of US history. Someone deliberately lied to you when they told you that and you chose to believe their dishonest version of the truth without questioning it.
If you can point to a single approved history textbook that calls Obama the greatest president of all time, I'll mail you a twenty dollar bill. If you find the very mention of bad things done by Americans to be evidence of a negative bias, I strongly suggest you stay away from history books, and from the news, and from the window.