Can you take me through this one? I think I know why it might be lower, but why would Nm be higher?

Warfare leads to genetic mixture through mate capture. And sometimes to settlement in conquered territories. Etc.

Can you take me through this one? I think I know why it might be lower, but why would Nm be higher?

in Consanguinity, Inbreeding, and Genetic Drift in Italy the Nm shot up in the 19th century across much of central and southern italy. this is because of better roads, which connected mountain villages which were previously separated by arduous treks.

My wife's great-grandfather in the Apennines was considered quite the romantic because he wooed a girl from the town 1500 feet below his mountain village.