Javelinas, better known as collared peccaries, are stopped at the US/Mexican border wall.
These javelinas are on the Arizona side of the border, but the wall stops them from coming into Mexico. The wall is not continuous across the border, so they can cross at other places.
So, at least theoretically, if we continue to extend the wall, we could unintentionally be the cause of speciation among the local peccaries and other wildlife?
It would have to have been up for a long time and very long.
I don’t think there was any speciatiion along the border between East and West Germany, which was also not entirely walled but very tightly guarded.