Okay, here we go:
(1) its just an idea. If you don't want to do it in your edit, that's cool. I'm just making a suggestion.

(2) this HAS happened before: it is what pretty much led to the destruction of the Roman Empire. We had this happen right before WW2 with Chamberlain and his "peace in our day" bit with Hitler. As far as 300 and EXCALIBUR the MOVIES, yes, they are myths of real events or myths of a forgotten past. While Frank Miller's account of the battle of Thermopylae didn't happen, the battle still did.

(3) The Republic is not a Nation State or a Federal State either; it is a banding of different worlds (countries) united in a republic, where every planet has representatives - you know, if the UN actually worked and everyone agreed to actually work together.

(4) Bingo, we all know that the "war on (islamic funded and backed) terror(ists)" is not a war on an "emotional state" and we do know that most Europeans just don't want to deal with it. Islamic terrorists exist - sorry to tell you this. Sheesh.

(5) If Mexico invaded Texas, the whole of the US would go to war? Really? 10 to 20 illegal immigrants who've been here for 10 to 20 years and are still mexican nationals, who have been tapping in to billions of tax dollars while being exploited by corporations and politicians? Not to mention the drug war that is happening in Mexico right now?

(6) as far as Texas invading Oklahoma (or some equivalent), that would have happened a long time ago (when state lines were first being formed) and if there was a "state-on-state" aggression, Union troops would have been sent to quell the fighting - there would be no investigation, just a straight-up army being sent.

Now what is interesting is that the American Civil War started because the Union general who was at Fort Sumter, South Carolina would not use force against the emerging Confederate army that was gearing up for there eventual attack on the fort. After the fort was taken, the general did nothing in response, which gave the Confederates the opinion that they had power and legitimacy to their claim(s). As a result, we had a bloody Civil War that may have well been ended if the US goverment stopped it right at the start.

I guess a better example would be how both the Americans and Europeans won't stop a lot of the atrocities that are happening in Africa. If Naboo is considered a "third world" planet, or of no importance to the Republic, why would they start a war with a competing super power over say, the Falkland islands or the planetary equivalent?