The Siamese Wars of Aggression were a series of conflicts that were started by Siam agianst its neighbors during the mid-19th century. Beginning in 1836, the Royal Siamese Army attacked and defeated the forces of Johore and Luang Prabang on multiple occasions, continuing sporadically until the late 1850s. Around that time, Siam also declared war on Dai Nam, which was assisted by its ally Cambodia. It lasted for about three years and saw an ultimate Siamese victory, but at a heavy cost, with a population loss of several thousand resulting from fighting on home territory.
Siam would later annex these states in a series of follow-up wars in the 1870s.