Who or what was a boomer? What gave rise to the boomer movement?

On the graph, the bottom horizontal line represents

When president johnson vetoed a law that would extend the freedmen’s bureau, congress reacted by supporting the veto and closing the freedmen’s bureau. writing a new law to show support for the black codes. overriding the veto and expanding the agency’s powers. drafting a law to prevent african americans from voting.

What misguided strategy caused lord william howe and the british to fail?