why does the military have their own court
Military justice The United States Constitution authorized the creation of a system of military justice. Article I, Section 8 permits the U.S. Congress to "make rules for the government and regulation of the land and naval forces."[26] Congress issued these rules first in 1806 as the Articles of War. Military justice during the American Civil War was governed by the 1863 Lieber Code. The Articles of War were superseded in 1951 by the Uniform Code of Military Justice (UCMJ).
Supreme Court of the United States The Supreme Court of the United States (sometimes colloquially referred to by the acronym SCOTUS)[2] is the highest federal court of the United States. Established pursuant to Article Three of the United States Constitution in 1789, it has ultimate (and largely discretionary) appellate jurisdiction over all federal courts and state court cases, involving issues of federal law plus original jurisdiction over a small range of cases. In the legal system of the United States, the Supreme Court is generally the final interpreter of federal law including the United States Constitution, but it may act only within the context of a case in which it has jurisdiction. The Court may decide cases having political overtones, but does not have power to decide nonjusticiable political questions, and its enforcement arm is in the executive rather than judicial branch of government.