I couldn't help but be struck by the simplicity of the verse phrase “a new king arose who did not know Joseph...” Some of the translations I found added phrases such as “who did not know Joseph or acknowledge all he had done.” But this is simply a commentary or expansion. The verse simply states that he did not know Joseph and this contributes, or perhaps even causes, his extreme reaction against the Israelites.
Historian George Santayana wrote that those who do not remember history are doomed to repeat it. Rabbi Alan Lew wrote that those who cling to tightly to history and don't let go of the story are also doomed to repeat it. We must somehow find a balance in each moment that allows us to acknowledge the past while remembering that we are living in the present. Pharaoh could not find that balance. He simultaneously chose to forget and to remember all too well the past, and this led to his fear that the Israelites might overwhelm him
There is no way to know for sure what caused Pharaoh to act as he did and to set in motion what ultimately became a great tragedy for him, his family and his nation. But if he had been able to be in the present and to find some sense of balance in terms of his memory of the past, without the ego playing its tricks, perhaps he could have welcomed the flourishing of the Israelites as a phenomenon that would have simply aided the flourishing of Egypt.
But alas, fear, ignorance and ego were his downfall, just as they are for so many of us. As we read this story let us remember that we all have the potential to act as Pharaoh did out of fear and ego. But if we allow our fear (which is a natural part of life) to draw us in rather than close us off, perhaps we will be able to see what is really beneath it all: the natural fear of the uncertainty of life. The ego reacts to this fear of uncertainty by striking out at anything that it might view as a threat. But if simply let go of the egos stories, we can embrace that fear, while also embracing the joy of living. Only then can we truly know and acknowledge the forces that have brought us to where we are and bless the moment with all of its contradictions and complication. If Pharaoh had done that, who knows how the story might have played out?