Which act organized the federal legal system and established the Supreme Court?

The Judiciary Act of 1789 is significant because it established the framework for the federal court system in the United States. This act created the Supreme Court and allowed for the establishment of lower federal courts, thus organizing the federal judiciary. It essentially filled in the details laid out in the Constitution regarding the judiciary's scope and structure, ensuring that there was a clear hierarchy within the court system. The act defined the jurisdiction of the Supreme Court and set the number of justices, which was initially set at six.

The other acts listed, such as the Sedition Act, Alien Act, and Neutrality Act, focused on different aspects of governance and national policy, including immigration and foreign relations. They do not pertain directly to the structure of the judiciary or the establishment of the Supreme Court, making the Judiciary Act of 1789 the correct and relevant answer for the question regarding the organization of the federal legal system.