Pretty sure it's outer core, lower mantle because the inner core is solid iron
Answer:
<u><em>River valley civilizations</em></u>
Explanation:
They were centred around various river valleys as their main source of livelihood and the flourished only due tiote river valley on which they were based. Like the harappan in Indus Valley, The yellow river (Huang He), the Mesopotamia around Tigris and Euphrates and the egyptian Nile.
Do you mean what caused it? or what the after affects where?
Uneven distribution of wealth, increased population leads to crowded urban areas which could be unsanitary, immigration can cause cultural conflicts
