What do you think the opportunities were that caused change?

Some are....

New land to grow croups on. Iowa for instance has amazing soil, so farmers are raising profit in that way of change.  Gold and silver being found was a huge deal and caused a lot of ruckus. This caused people to get wealthier, become leaders in business to maintain those mining plants, and also started up railroads along the way.  Railroads were created later on for transportation of people, goods, and many other things.  From the those railroad opportunities people gained more jobs. Most of the change caused many people to have the opportunity to become wealthy, have a job, better business, better homeland for families to grow, ect...