Birmingham, alabama, was chosen by civil rights activists as a site for major demonstrations in april 1963 because

It was chosen by Civil Rights Activists as a site for major demonstrations in April 1963 because they considered it "the most segregated city" in America.

They made a checks and balance system to equal power within the branches. the "check" meant that one branch would watch one branch and "balance" them if they were too powerful. if you want more info on this, i would just google checks and balance system.