Add a National Guard rank that would work like sheriff rank but on a scale of a nation.
Bassicly the rank would allow nation members to attack outlaws in other towns that are part of their nation.

For example player1 is outlawed in town B player2 is a part of town A in the same nation as town B the rank would allow
player2 to attack player1 in town B

Another approach for this could be adding /n outlaw command along the rank where a player can be outlawed in all nation towns
and killed by members holding the rank