Your picture is to blurry
It was the landmark case "Marbury vs. Madison" that allowed the Supreme Court to claim the power of judicial review (the authority to declare a law unconstitutional), since this now acts as one of the major "checks" the court has on the legislative branch.
Albeit this is a basic answer, World War Two was a major catalyst to an increased focus on internationalism. In addition, financial and political interests (most notably for political interests is the Cold War) are both legitimate reasons to why the United States of America has remained as a major part of international affairs.
The name of the case was Plessy vs. Ferguson. Hope this helps :)
