Other 2 answers describe current situation, but the origin is much older. In 1699 Repubublic of Ragusa (now Dubrovnik) ceded Neum to the Ottoman Empire, to prevent land attack from Venice, as Dalmatia was part of Venice that time. Than BiH and Croatia just inherited the borders.
Other 2 answers describe current situation, but the origin is much older. In 1699 Repubublic of Ragusa (now Dubrovnik) ceded Neum to the Ottoman Empire, to prevent land attack from Venice, as Dalmatia was part of Venice that time. Than BiH and Croatia just inherited the borders.
https://en.m.wikipedia.org/wiki/Neum#History