How many territories are there in the region with the highest number of territories?
highest number of territories refers to max(TerritoryID)
SELECT COUNT(T2.RegionDescription), T1.TerritoryDescription, COUNT(*) AS num FROM Territories AS T1 INNER JOIN Region AS T2 ON T1.RegionID = T2.RegionID GROUP BY T1.TerritoryDescription ORDER BY num DESC LIMIT 1