See code in Sheet1's code-module in the attached.
It will work on the entire column A/B of Sheet1, whether or not there's a dropdown in either column A or B, but only if it detects one of the countries in the table.
This is the code:
Private Sub Worksheet_Change(ByVal Target As Range)
Dim ColumnACells As Range
Set ColumnACells = Intersect(Columns(1), Target)
If Not ColumnACells Is Nothing Then
For Each cll In ColumnACells.Cells
zzz = Evaluate("VLOOKUP(""" & cll.Value & """,Sheet2!$A$1:$B$5,2,FALSE)")
If Not IsError(zzz) Then cll.Offset(, 1) = zzz
Next cll
End If
End Sub