Religion caused many Arabs to move through the Middle East.
During the 600s CE, an Arab expansion took place all over the Middle East. During these years, Muslim conquests became common, and this led to the establishment of unified Arabic empires, or "caliphates."
The length of daylight and nighttime are of equal length on an equinox because the center of the sun spends a roughly equal amount of time above and below the horizon at every location on the Earth.
The Indus valley thrived between 4000 and 1500 BC
