Answer :
the incorporation of the first,fourth,and sixth amendments of the bill of rights
What the three cases have in common is that they were all victories for the people and their amendment guaranteed rights against states who wanted to obstruct those. The first case was about preventing states from limiting freedom of speech, the second was about preventing illegally obtained evidence from being used in court, and the third was that the states have an obligation to provide a lawyer to criminals if they can't pay for them.
