index=* SrcCountry=Mexico
| timechart span=1week count by SrcCountry
This gives you a count by Country per week.
Run the search across 2 weeks. (If you want complete weeks you can "snap down" to the nearest week by using span=1w@w)
Or,
index=* SrcCountry=Mexico
| timechart count by SrcCountry span=1d
| timewrap 1week
This returns a daily count by country, that is compared to the previous week days.
I used Mexico as the example country. Any countries with spaces need quotes: like "United States"