Everyone wants to claim Lincoln for his own. Overall, he kept the US strong and unified for its future role in the future as the final guarantor of peace in the world. If the US had had a somewhat hostile southern neighbor it would never have had the freedom of maneuverability to intervene in a timely and casualty-friendly manner in world affairs and dominate the 20th century so much.
And the inclusion of the south has kept the politics of the country right-ward even when the rest of the western world was going gonzo for socialism. Well until the election of Barry. Now we’re just running out the clock until the US is a socialist hellhole just like France.
I think a communist hellhole like Cuba or Zimbabwe is even more likely.
U.S. intervention in Europe hasn't exactly been a brilliant success. Wilson got us into WW I, where our so-called Allies imposed a brutal peace on Germany which led directly to WW 2, which in turn saved Stalin and enslaved millions, leading directly to the Korean War, Vietnam War, Cuban missile crisis, etc.
Washington explicitly warned us not to get involved in the endless vendettas of the European powers.