War and armed conflict — War crimes — Definition — Trial of unlawful alien enemy combatants before military commissions — Conviction by military commission for “material support for terrorism” — Military Commissions Act 2006 specifying “material support for terrorism” as war crime — Conviction based on conduct occurring during 1996-2001 — Direct appeal of a military commission conviction — Whether Military Commissions Act 2006 retroactively punishing new crimes — Whether relevant statute at time of conduct authorizing prosecution for “material support for terrorism” — Relevant statute authorizing prosecution for violations of “law of war” — “Law of war” meaning “international law of war” — Whether “material support for terrorism” a war crime under international law — Whether any relevant treaties — Whether customary international law making “material support for terrorism” a war crime — The law of the United States