How did the Great Plains across the Mississippi river become a major wheat-producing area of America?

(i) In the earl,v years, the fertile soil produced good crops.
(ii) When the soil used to get exhausted, the migrants would move further
west to explore new lands to raise a new crop.
(iii) When the migrants reached the Great Plains across the Mississippi river,
they settled down as this region, in few decades, became a major wheat-producing
area of America.