88 EARLY CHOSON DYNASTY
cial weakness in Korea's defense against the Japanese but more from failure of
the top leadership to throw their forces into blocking the Japanese advance at
the Han, Imjin, and Taedong rivers.
As opposed to the Sung dynasty (960-I280), the Eastern Chin had established
afan-chen system of frontier garrisons that combined several civil districts in
one military district with a large garrison (ta-chen) under a single commander.
This provided unified command over a large force. The reason the Sung had not
followed this earlier precedent was because they feared the build-up of regional
power by commanders such as An Lu-shan of the T'ang. Thus, they abolished
the fan-chen and kept provincial forces subdivided according to the usual civil
districts, the chiin and hsien. Because these units were too small and weak, the
enemy picked them off one after the other.84 The point was an important one:
since Sung overreaction to the power of the military in the T'ang era had led to
fragmentation of forces and weakening of the army, Yu was suggesting that a
similar factor might have operated in Korea's current military weakness. Some-
how, a balance had to be found between civilian control and military strength.
Ch'i Chi-kuang's System and Sen'ice for Slaves. Yu Songnyong was also a
leading advocate of Ch' i Chi-kuang's Che-chiang system of military organiza-
tion, which incorporated soldiers trained in firearms and muskets into the reg-
ular army, but the key organizational principle of the system was simply to divide
large forces into small units, arranged in an ascending hierarchy. The term sago
(Korean pronunciation), was the label for this method of organization described
in the first chapter of Ch'i Chi-kuang's Chi-hsiao hsin-shu, and it became the
basis ofYu Songnyong's military reorganization adopted between 1594 and 1596
by the order of King Sonjo.~5
The sogo system also broke the main barrier against the full mobilization of
the male population for national defense by providing for the recruitment with-
out respect to status. Men of base status. that is official or private slaves, and
male nothoi of yangban (sool) were included in troop units alongside men of
good status (yang'in). Their masters wcre compensated by the grant of either
office rank or a substitute slave.^86
On January 25, 1594, during the armistice, King Sonjo ordered the recruit-
ment of all men exempted from military service (myonyok) and freedmen
(myonch 'On), and formed all slaves in the capital city into companies, a policy
he had refused to adopt during the suppression of rebellion in 1583.87 After the
war in 1600 and 1602 he also manumitted slaves and recruited them into the
military, used male slaves employed in the palace (naeno) to fill military vacan-
cies in thirteen towns. and recruited private slaves of yangban to serve as archers
(sasu). Although he reversed this policy and returned private slaves to their mas-
ters in 1603, the sogo system by which slaves were recruited into military ser-
vice stayed in place for the last half of the dynasty.88
The new sago troops were organized into squads of 1 I men, platoons or ban-
ners of 33, companies of 99, battalions of 495, and divisions of 12,375.^89 It is
unclear just what the relationship was between villages and districts and sogo