It is interesting that this is being discussed in modern times, but it is probably a great idea to talk about it. Is the US Declaration of Independence illegal? A portion from the article:
For American lawyers, the answer is simple: “The English had used their own Declaration of Rights to depose James II and these acts were deemed completely lawful and justified,” they say in their summary.To the British, however, secession isn’t the legal or proper tool by which to settle internal disputes. “What if Texas decided today it wanted to secede from the Union? Lincoln made the case against secession and he was right,” they argue in their brief.