Lincoln laid the groundwork for public support in an open letter published in response to Horace Greeley's "The Prayer of Twenty Millions"; the letter stated that Lincoln's goal was to save the Union, and that, if he freed the slaves, it would be as a means to that end. He also had a meeting at the White House with five African American representatives on August 14, 1862. Arranging for a reporter to be present, he urged his visitors to agree to the voluntary colonization of black people. Lincoln's motive for both his letter to Greeley and his statement to the black visitors was apparently to make his forthcoming Emancipation Proclamation more palatable to racist white people. A Union victory in the Battle of Antietam on September 17, 1862, provided Lincoln with an opportunity to issue the preliminary Emancipation Proclamation, and the War Governors' Conference added support for the proclamation.