As an outspoken opponent of the expansion of slavery in the United States,Lincoln won the Republican Party nomination in 1860 and was elected president later that year. During his time in office, he contributed to the effort to preserve the United States by leading the defeat of the secessionist Confederate States of America in the American Civil War. He introduced measures that resulted in the abolition of slavery, issuing his Emancipation Proclamation in 1863 and promoting the passage of the Thirteenth Amendment to the Constitution, which passed Congress before Lincoln's death and was ratified by the states later in 1865.