Mongol expansionismThe projection of Mongol power
The Mongols had conquered Yunnan as part of a grand strategy to out-
flank the Southern Song, rather than to extend the Chinese empire
into Southeast Asia. The danger posed to the independent kingdoms
of Southeast Asia was soon apparent, however. Using Yunnan as a
base the Mongols intended to sweep south and east through northern
Vietnam to threaten Canton. When in 1257 permission for their
forces to pass through Vietnamese territory was refused, a Mongol army
mounted a swift invasion. The Vietnamese capital of Thang-
long (modern Hanoi), was seized and sacked, but the Vietnamese
resorted to guerrilla warfare, and as climate and disease took their
toll, the Mongols were forced to withdraw. Southern Song resistance
continued for another twenty years. Vietnam’s punishment was to
come later.^4
On his succession to power in 1260 as both emperor of China and
Khan of Khans, Khubilai determined to bolster his legitimacy through
enforcing the submission of tributary states, by conquest if necessary.
Though still engaged in subduing the Southern Song, Khubilai
notified all kingdoms tributary (in theory) to China that a new
dynasty had received the mandate of Heaven, and called not just for
appropriate tribute to be offered, but for submission in person by the
ruler. Particular attention was paid to Vietnam. In 1267, Khubilai
demanded not only the Vietnamese king’s personal submission, and
that his sons should reside in Beijing as hostages, but also that a pop-
ulation census be carried out to serve as the basis for taxation and
military corvée(forced labour owed to a feudal lord), and that a
Mongol governor be appointed. For the Vietnamese these conditions
were quite unacceptable, for they amounted to de facto loss of Viet-
namese independence. The Vietnamese parried these demands, while
continuing to send the usual tribute missions; but they were playing a
dangerous game. States that proved uncooperative, as did Japan,
could expect retaliation. Mongol fleets invaded Japan in 1274 and