When people are oppressed by their government, it is a natural right they enjoy to relieve themselves of the oppression, if they are strong enough, either by withdrawal from it, or by overthrowing it and substituting a government more acceptable.
 Ulysses S. Grant, Personal Memoirs of Ulysses S. Grant (1885). copy citation

Context

“yet, if separation had actually occurred, Texas must necessarily have gone with the South, both on account of her institutions and her geographical position. Secession was illogical as well as impracticable; it was revolution. Now, the right of revolution is an inherent one. When people are oppressed by their government, it is a natural right they enjoy to relieve themselves of the oppression, if they are strong enough, either by withdrawal from it, or by overthrowing it and substituting a government more acceptable. But any people or part of a people who resort to this remedy, stake their lives, their property, and every claim for protection given by citizenship—on the issue. Victory, or the conditions imposed by the conqueror—must be the result.” source