Well the logistical statement would look like:
But doing that for 18 cities and 11 countries wouldn't be ideal.
So let's try VBA.
In the code below I show how it is done for one city (London > UK) and for multiple cities (Tokyo / Hiroshima > Japan).
Expand the code below with your city/country list:
Private Sub Worksheet_Change(ByVal Target As Range)
If Intersect(Columns("A:A"), Target) Is Nothing Then Exit Sub
If Target.Value Like "*London*" Then Target.Offset(0, 1).Value = "UK"
If Target.Value Like "*Tokyo*" Or _
Target.Value Like "*Hiroshima*" Then Target.Offset(0, 1).Value = "Japan"
To use the code, right-click on the sheet's tab and select View Code and paste the code in the big white field.
The code will now run automatically, so update or enter data in column A and column B will show the country.
Let me know how this works out for you.