Linked from
The 10 pages that link to Siam, each with the reason it gives.
Rama INarrower topic: Rama I ruled this kingdom before the modern Thai state existed.
PrajadhipokNarrower topic: Prajadhipok ruled this kingdom during a period of political transition.
VajiravudhNarrower topic: Vajiravudh ruled Siam before the country adopted the name Thailand.
Rama IINarrower topic: Rama II ruled the kingdom historically known as Siam.