People often think that single edge and curvature are attributes of Japanese blades, thus south east asian must have borrowed those elements from the Japanese. However, there are many solid evidence pointing out that the curved blade has been around in this region ages prior to first contact with Japanese.
For example, this is a 13th century blade from Vietnam : the way the hilt is not detachable from the blade is fundamentally different from the common Japanese blade
Hi res picture
http://i722.photobucket.com/albums/w...a/DSC04505.jpg