Final answer:
Early American civilizations and the River Valley civilizations both developed agriculture facilitated by major rivers, which provided the foundation for stable, sedentary societies and the emergence of complex cultures.
Step-by-step explanation:
One similarity in the development of Early American civilizations, such as those in the Ohio River valley, and River Valley civilizations, including those like Ancient Egypt and Mesopotamia, is their reliance on agriculture sustained by proximity to rivers. Both sets of civilizations were fundamentally agrarian, utilizing the fertile land along rivers like the Nile, Tigris, and Euphrates, as well as those near the Yangtze and Yellow Rivers in China, to support large, sedentary populations.
The stability offered by agricultural surpluses allowed these societies to develop intricate cultures, with specialized artisans emerging alongside the ruling class, reflecting their power through decorated pottery, ornate structures, and other creative works.