Final answer:
Ancient Mississippi civilizations were greatly affected by the Tigris and Euphrates rivers, as they provided water for irrigation, served as transportation routes, and influenced the development of complex societies.
Step-by-step explanation:
Ancient Mississippi civilizations were greatly affected by the Tigris and Euphrates rivers in several ways. Firstly, the rivers provided a source of water for irrigation and agriculture, allowing the civilizations to grow crops and sustain their communities. Secondly, the rivers served as transportation routes for trade and communication, enabling the civilizations to engage in economic activities and interact with other communities. Lastly, the rivers influenced the development of complex societies and civilizations, as the need to manage the rivers and protect against flooding led to the formation of larger-scale settlements and systems of governance.