Why did so many of these early civilizations emerge along major river valleys? Which was the most successful?

Why did so many of these early civilizations emerge along major river valleys? Which was the most successful?For Section One, read pp. 2-137 in the Grafton and Bell text, Articles #1-11 in the Bridges text, and the online lectures. For Section Two, continue the online lectures and read pp. 137-318 in Grafton and Bell and Articles #12-24 in the Bridges text. For the last section, finish the online lectures and read pp. 318-470 in Grafton and Bell and Articles #25-32 in Bridges.Participation: Online participation in the discussion boards will be required. Students must participate in discussion boards, leaving a main post directly responding to the question (these posts must be 150-200 words long with a bibliography) and at least two follow-up posts responding to either other student posts or instructor posts. The times these posts are to be left is up to the student, but the posts for the week must be completed by each Sunday night at 11:59 PM. Participation will be asynchronous, that is, no formal class times will be required, but students must participate a set amount of time each week. Discussion board comments will be based on questions posted by the professor and the class readings. Each discussion question each week will count 5 points toward the student’s final grade (including the main post and two follow-up posts) for a possible 15% total for the semester. New questions will be posted each week. Questions regarding exams and participation can be sent to the professor at *********************.1.What was the most important invention before 4000 BC?