Under British law in 1776, yes it was illegal. That why a war was fought to break away from the mother country and institute our own laws and Constitution, including a Bill of Rights.
Under German law in the 1930s, seizing the property of Jews, placing them in camps and slaughtering them was legal. That's the funny thing about laws. Just because something is illegal, it isn't necessarily wrong. Just because something is legal, it isn't necessarily right.