Here is a good answer I found online--->
Six million Jews were murdered by the Nazis, and this figure comes from the Nazis themselves, who were meticulous about recording their atrocities.
In 1945, General Dwight D. Eisenhower, Supreme Allied Commander, anticipated that someday an attempt would be made to recharacterize the Nazi crimes as propaganda and took steps against it:
“ The same day I saw my first horror camp. It was near the town of Gotha. I have never been able to describe my emotional reactions when I first came face to face with indisputable evidence of Nazi brutality and ruthless disregard of every shred of decency. Up to that time I had known about it only generally or through secondary sources. I am certain however, that I have never at any time experienced an equal sense of shock.
I visited every nook and cranny of the camp because I felt it my duty to be in a position from then on to testify at first hand about these things in case there ever grew up at home the belief or assumption that "the stories of Nazi brutality were just propaganda". Some members of the visiting party were unable to go through with the ordeal. I not only did so but as soon as I returned to Patton's headquarters that evening I sent communications to both Washington and London, urging the two governments to send instantly to Germany a random group of newspaper editors and representative groups from the national legislatures. I felt that the evidence should be immediately placed before the American and the British publics in a fashion that would leave no room for cynical doubt."
Denials of the Holocaust have been regularly promoted by various Arab leaders and in various media throughout the Middle East. Newspapers funded by the Saudi Arabian government routinely deny the existence of the Holocaust, or downplay its significance. Individuals from the Syrian government, as well as the Palestinian political group Hamas have recently published Holocaust denial statements.
In August 2002, the Zayed Center for Coordination and Follow-up, an Arab League think-tank whose Chairman, Sultan Bin Zayed Al Nahayan, served as Deputy Prime Minister of the United Arab Emirates, promoted a Holocaust denial symposium in Abu Dhabi. Hamas leaders have also promoted Holocaust denial; Abdel Aziz al-Rantissi held that the Holocaust never occurred, that Zionists were behind the action of Nazis, and that Zionists funded Nazism. A press release by Hamas in April 2000 decried "the so-called Holocaust, which is an alleged and invented story with no basis."
Holocaust denial has also been resisted by prominent intellectual figures in the Arab world; in 2001, an outcry led by Palestinian poet Mahmoud Darwish, Lebanese writer Elias Khoury and others brought about the cancellation of a conference the Holocaust denial organization Institute for Historical Review had planned to hold in Beirut.
In 2005 the Egyptian Muslim Brotherhood leader, Mohammed Mahdi Akef, denounced what he called "the myth of the Holocaust" in defending Iranian president Mahmoud Ahmadinejad's denial of the Holocaust.
According to the Associated Press, "Ignorance and even denial of the Holocaust is widespread in Palestinian society