The Jewish Encyclopedia: 'David waged a sacred war of extermination against the Amalekites.'
Throughout the history of Judaism and the nation of Israel the memory of the Amalekites has never truly been blotted out. Though the story of their annihilation may be hard to retell with historical facts to back it up, the tale of their demise has lived on. Mainly in part to its repeated mention throughout the Torah.
Numbers 24:20 "Then he looked on Amalek and took up his discourse and said, 'Amalek first among the nations, but it ends in utter destruction.'"
It is in these accounts of the battles against the Amalekites that the ancient Israelis are often seen as killing ruthlessly this opposing tribe. It is in the Torah that the accounts note that G-d commanded of Israel to not only kill the men of Amalek who took to the battlefield but also to slaughter all of the Amalekite women, children, infants, and even their animals. And it is in these accounts that we can not ignore the fact that this act would today be called genocide.
"Now go and strike Amalek and devote to destruction all that they have. Do not spare them, but kill both man and woman, and infant, ox and sheep, camel and donkey." 1 Sam. 15:3
Today Christians and Jews alike write off the genocide of the Amalek people. Many claim that G-d himself commanded the actions of Israel so the killing is totally without blame. Others just simply consider the genocide part of ancient history.
I myself can not answer the questions this subject brings to the surface. I will not attempt to place the blame with my G-d. I will not squarely place the blame with the ancient Israelites. But unlike most of my fellow believers, I will give this ancient tribe its justice in admitting that this was genocide.
It is also important to note that no religion or race of man today can say that their ancestors have not done the same. Wherever we look in history there are accounts of genocidal wars and what would be called ethnic cleansing today. Islam started out with clear cases of ethnic cleansing in Arabia. Christianity spent countless years of "crusading" to rid the world of opposing views in both recent and ancient times. Buddhism has been used to justify ethnic cleansing in places like Myanmar every since it's spread. And Judaism has recorded it's own cases of genocide throughout the Torah.
It is only when we can accept this part of our own history that we can fully accept our past in its entirety. And when we finally accomplish that we can begin to take meaningful steps to end this grotesque chapter in our history as a species.