The main reason many American Indian groups moved west was to
avoid the encroachment of Spanish settlers,
escape the imposed system of repartimiento,
find more fertile land and better weather for planting,
find larger pieces of land for their growing population,
The answer is find larger pieces of land for their growing population
Explanation: Native Americans want a better way of living, so they move west, looking for more land and better conditions for their families, as well as for those who grow up.
