You think the two world wars were started by Democratic presidents? Seriously? By your criteria, that the president in office at the time a war occurs is the one who started it, then Lincoln, a Republican, started the Civil War. After all, he didn't have to attack the south just because they wanted to be a separate nation, right?

You left out the GOP's Spanish-American War and the Philippines War.

The Civil War was started by southern racist secessionists. Their descendants today vote Republican. The Democratic Party consisted of both pro-slavery southerners and anti-slavery northerners, which is why there were two Democratic nominees in 1860, before the Civil War, Stephen Douglas from Illinois and John Breckinridge of Kentucky. The Democratic Party in the 1860 Charleston convention voted down a pro-slavery plank, which is why a rump group of southerners, like the Dixiecrats of 1948, broke away with their own convention and nominated Breckinridge.