Early civilizations of the Indus Valley: had clever city planners
had weak governments and strong armies
declined mainly due to natural disasters
had thriving farms that allowed job specialization
had strong central governments
and were relatively sophisticated

Tides are caused by a differences in the gravitational force of the sun at different points on earth. differences in the gravitational force of the moon at different points on earth differences in earth’s gravitational field strength at different points on earth’s surfac fluctuations in the gravitational attraction between earth and the moon.