On December 6, 1865 the Republican Party abolished slavery.
Grand Old Partisan reported:
On this day in 1865, the 13th Amendment — abolishing slavery — became part of the Constitution — when ratified by three-quarters of the states.
Despite protests from the Democrats, the Republican Party made banning slavery part of its national platform in 1864. Senator Lyman Trumbull (R-IL) wrote the final version of the text, combining the proposed wordings of several other Republican congressmen.
All Republicans in Congress voted for the 13th Amendment, while nearly all Democrats voted against it. So strongly did President Abraham Lincoln (R-IL) support the 13th Amendment, he signed the document, though presidential approval is not part of the amendment process.
Yes, outlawing slavery was a Republican achievement.