The key event that is missing in the timeline for the New Kingdom (1550–1069 BCE) is likely the military campaigns against the Hittites and Mitannians in Palestine. This period saw significant military engagements by the Egyptians in the Levant, including conflicts with these powers, which played a crucial role in the history of the New Kingdom. Therefore, the best answer is:
Hittites and Mitannians in Palestine.