The crisis between 1850 and 1860 brought Lincoln's ideas before larger groups. Until that year the Democrats had apparently remained united. At the Democratic National Convention in Charleston, South Carolina, in April, 1860, there was a division.[14] The Northern Democrats, unable to comply with the demands of the slave power that the convention should adopt a platform requiring Congress to protect slavery in the territories and the Northerners to acknowledge and advocate the moral right of slavery, forced the South to the radical position of withdrawing from the Convention. Since no candidate could then be nominated, the Convention adjourned to Baltimore, in the hope that time would bring about a reconciliation; but in the end the Northern Democrats nominated Douglas, and the Southerners nominated Breckenridge.[15] The Republican Convention was held in Chicago in May 1860, and there was adopted a moderate platform, with a denial of the right of Congress to interfere with slavery in the States. The Republicans reaffirmed the Declaration of Independence and declared that Congress should prohibit slavery in the territories. They repudiated the Dred Scott decision and advocated a protective system. Their most difficult problem was the selection of a candidate for the presidency. Inasmuch as Seward and Chase had alienated certain elements by their bold advocacy of advanced principles and Lincoln was comparatively unknown, the managers of the party finally accepted him because of his availability. This choice was received with much indignation among the antislavery leaders, for even Wendell Phillips and William Lloyd Garrison railed against the nominee and portrayed him as an obscurity.[16] Lincoln's election forced slavery into the foreground. Without waiting for his inauguration, several Southern States, acting in accordance with their previous threats that they would secede if a Republican President were elected, withdrew from the Union. Others soon followed their example. Congress hastened to offer various concessions to the seceding States,[17] but these efforts for compromise were in vain. The die was cast. When Lincoln asserted that his oath of office bound him to preserve the Union at any cost, civil war became inevitable. The proslavery element opened fire on the American flag at Fort Sumter and forced its surrender April 14.[18] On the next day Lincoln issued a proclamation calling for 75,000 volunteers. 500,000 others were later called to defend the honor of the nation.