The Manual:
page 12:
Important Note: In order to gain credit for a captured Objective or Strategic City, a player must garrison the
location with a regular unit of infantry or cavalry (i.e. no Irregulars, Militias) if the region has a Loyalty Rating less
than 51%.
page 56:
Note however, that Victory Points are not gained from Objective/ Strategic Cities in regions with less
than 6% Loyalty (i.e. hostile territory) unless the cities are garrisoned.