Tenochtitlan is not in the US, and was in ruin by the time the US was founded. It is in Mexico, near Mexico City, and was a major center for the Aztecs.
what and barley
The crops you can grow near the equator are sweet potato, tea, rice, durians ,chilli, mangoes, basically some tropical fruits, some starches.
plants
wheat and grain
They did that so they can grow crops
Most of the West African farmers grow crops on community land. Villages have small land patches where anyone in the village is free to grow crops. A lot of the crops are used for subsistence.
because of the abundance of good land near rivers to grow crops
Because when the rivers flood then the farmer's crops can get water and they can grow.
They live near volcanoes because the land is very fertile and they can grow crops after the eruption.
The land is usually good to grow crops on. It is rich in minerals and with care it can produce abundant crops.
Crops grew well in Mesopotamia because it was located near the fertile crescent which had rich fertile land