.......the war is not waged in any spirit of oppression, or for any purpose of conquest or subjugation, or the overthrowing or interfering with the rights or established institutions of those (Southern) states, but to defend and maintain the supremacy of the Constitution, and to preserve the Union with all the dignity, equality, and rights of the several states unimpaired........as soon as these objects are accomplished, the war ought to cease.
McClain’s Own Story
Twenty Years of Congress from Lincoln to Garfield
According to "Private Life & Public Services of Salmon P Chase" this did not sit well with the Republican party. They were afraid they would lose their newfound strength.