Laos and Thailand have been in culturally, politically and economically deep mutual relations. Histories of both states have been closely intertwined in many aspects. In their mutual historical relations, the Thai have often regarded Laos as a country which is dependent on or even subordinate to Thailand. It seems that they generally look down upon the Lao, while the Lao have a kind of cultural or psychological complex toward the Thai. Such a relationship seems to be also reflected in perception and assessment of mutual historical relations,especially those between late eighteenth and early nineteenth century. Siam attacked and occupied Lan Xang in late eighteenth century, reducing it to a vassal status. Lan Xang, under the leadership of Anouvong, king of Viangchan, ventured a resistance against the Siamese rule in the 1820s, which was suppressed by the Siamese army. Lan Xang remained a colony of Siam until 1893, when Siam ceded the territory of Laos to France. The Thai in general have been regarding the military resistance of Lan Xang as a rebellion, while the Lao call it "an independence war." Such a difference in historical assessment can be also ascertained in history text books of both countries. The following aspects have to be considered in comparing historical perceptions on relations between Laos and Thailand. The Thai seem to have a consciousness as injurer toward Laos,which they ruled as a vassal more than one hundred years, and whose resistance they cruelly suppressed. The Lao historiography in comparison, seems to pay more attention to the ethnic and cultural differences and boundaries between Laos and Thailand. They seem, at the same time, to try to bring to the fore the inflictions the Thai did to the Lao. It appears that they in this way attempt to strengthen the national identity vis-a-vis the Thai.