Lincoln, Abraham(1809-1865) (USA Civil War President 1861-65) 5

If Lincoln had decided to let the South secede, it's hard to say exactly what would have happened. Maybe the CSA would have rejoined the Union after a few decades, or maybe they would still be two countries. It's also possible that if it was decided that states do have the right to secede, that maybe there'd be three or more countries by now. Maybe the west coast would have broken off and done it's own thing, who knows? Alaska might still be Russian, or maybe they would have eventually sold it off to Canada, and who knows about Hawaii, Japanese maybe?

Regardless of the exact outcome, it would have meant huge differences in world events during the 20th century. Would the USA have gotten involved in WWI? Maybe the USA and CSA would have taken different sides. How about WWII? Of course if the Germans had won WWI, there might not have even been a WWII. Would the old USSR even have existed in the form we knew it? Maybe not if Germany had ended up controlling a good chunk of Eastern Europe.

It's impossible to know what would have happened, whether things today would be better or worse had Lincoln not made certain decisions, but the world would be a different place.