Egypt and the Egyptian people have always been culturally and politically (and even physically) distinct from other African peoples (though it is important to note that Africa is a HUGE continent with a huge amount of variance among its cultures), and have always been tied sociopolitically to the Middle East, as far back as even the Old Kingdom. There hasn't been some distinct event or chain of events that made this happen.

But we can say that a distinct event led to the inclusion of Egypt within the solidified Arab world - the Islamic conquests of the seventh century that occurred first under Muhammad and continued under his succeeding caliphs.