unified the German States into Germany
limited government means less ideas
"Byzantine weakness allowed the Ottomans to capture much Byzantine land" would be the best option from the list, since the Byzantines had spread out their sphere of power to an extent that it was unable to govern properly.
Because a pandemic(unlike and epidemic, which is more provincial) reaches around an entire nation and/or continent. Obviously, a nationwide sickness would be terrible for a newly developing nation trying to get on its feet for the first time. It’s just more unnecessary work for the new nation to deal with. Hope this helps!