How does the study of law and legal structures help us understand the history of the United States in the twentieth century?

So, in the twentieth century there was a positive explosion of law. Coming out of the ultra restrained nineteenth century where not a single case about the First Amendment was heard by the courts, the United States witnessed demands for economic and social engineering to meet the needs and expectations of an urban industrial population. Three major time periods saw a burst of legal energy that changed the direction of the country: The Progressive Era from 1900-1914, the Great Depression from 1919 to 1937 and the 1960s which was a remarkable decade of social activism in defense of human rights. My answer is focusing on landmark cases like Lochner to Brown v. Education Board to Baker v. Carr. I just want more insight on the same or different point of view to further my understanding.