Invading armies flew the Nazi Flag.
During the War Between the States, the invading armies flew the Stars and Stripes.
The principle, on which the war was waged by the North, was simply this: That men may rightfully be compelled to submit to, and support, a government that they do not want; and that resistance, on their part, makes them traitors and criminals. No principle, that is possible to be named, can be more self-evidently false than this; or more self-evidently fatal to all political freedom. Yet it triumphed in the field, and is now assumed to be established. If it really be established, the number of slaves, instead of having been diminished by the war, has been greatly increased; for a man, thus subjected to a government that he does not want, is a slave. And there is no difference, in principle --- but only in degree --- between political and chattel slavery. The former, no less than the latter, denies a man's ownership of himself and the products of his labor; and asserts that other men may own him, and dispose of him and his property, for their uses, and at their pleasure. – Lysander Spooner (Nineteenth-Century Yankee lawyer, abolitionist)