After the election of Abraham Lincoln and the secession of several Southern states in 1860, Van Buren unsuccessfully sought to call a constitutional convention. In April 1861, former president Pierce wrote to the other living former presidents and asked them to consider meeting to use their stature and influence to propose a negotiated end to the war. Pierce asked Van Buren to use his role as the senior living ex-president to issue a formal call. Van Buren's reply suggested that Buchanan should be the one to call the meeting, since he was the former president who had served most recently, or that Pierce should issue the call himself if he strongly believed in the merit of his proposal. Neither Buchanan nor Pierce was willing to make Pierce's proposal public, and nothing more resulted from it. Once the American Civil War began, Van Buren made public his support for the Union.