What changed in the US after reconstruction was a rise of imperialism?

So are you asking what major change happened in the US
after Reconstruction?

If that is what you are asking, the
rise of imperialism is one possibility.  However, I would say that the real rise in
imperialism does not start for around ten years after Reconstruction ended in
1876.

Another change that was happening in the US right
after Reconstruction was an increase in conflict between workers and employers.  This
played out partly in strikes, some of which were quite
violent.

The increase in labor conflict was tied to a boom
in the US economy and an increase in the size of companies.  This is another major
change in the US after Reconstruction.  However, it was already happening before
Reconstruction ended.