It's not like the us military has had some unchanging set of rules. Throughout the last 50 years public ethics policy has vastly changed how the military functions and will continue to do so.
The armed forces may not be a democracy but they exist by the grace of our democracy.
The rules against releasing classified information are in no way arbitrary and have been long-standing parts of military and foreign affairs since their inception. There has been no time when releasing an indiscriminate cache of State Department cables would have ever been considered a legal gray area. (Indeed, the confidentiality of diplomatic communication has been a norm that has existed for thousands of years: http://isanet.ccit.arizona.edu/noarchive/jonsson.htm). Manning very clearly broke the law and could not have failed to know that he was breaking the law.
policy has changed in regards to gays and females in the military, yes. but where exactly has there been policy impact when it comes to the ones of the receiving end of the military force? the US bombs people all over the world, all the time, women, children, no problemo. not a US citizen, no rights at all.
hypocrisy. "the grace of your democracy guides the US Armed Forces". HORSESHIT.
in the civil justice system there are laws. if you break them, you get punished. some of them have special rules around them. take murder. kill someone, go to jail. but if it was self defence, you might walk. easy, right?
in the military justice system, leaking classified docs is a punishable offence. there is no way around this. there is no self defence, etc alternate way. you break the rule, you get court martialed. morals, ethics do not come into play here.
as a soldier, your interpretation of your oath does not apply here. it would when refusing orders like "kill those civilians over there", but only maybe and not in the way you'd like. again, military justice is not following the same framwork of rules and ethics you're used to as a civilian.
the armed forces in itself are not a democracy. they are a special area of society that exist to provide the ability to kill other humans. in order to do so anything civilian quickly goes out the window. the rules exist to enforce the most optimal sytem to maintain a killing force, not the well being of the individual within the organization.
if you don't like that, you should campaign for complete disarmament and the complete disassemblement of the armed forces. there is no half-way, grey area. once you have an army, it exists to kill humans, with all the consequences. the hero whorship present in the US around any soldier seems to imply that the US society has forgotten this (and then is surprised once something like the sentencing of Manning happens).
Nuremberg does not apply at all here. German officers were tried by the Allied Forces, not their own Army. This was the victors cleaning up. The US has not joined the International Criminal Court for similar reasons, to prevent other nations prosecuting its officers and soldiers (for war crimes, etc.). If you want to do so, you'll need to invade the US and be the victor. Note that Saddam was tried and sentenced by an Iraqi court, not an international tribunal even though US soldiers caught him.