How are Thai and Siam different?

Thai is a major ethnic in Thailand (Siam), Siam mean dark people. Siam is a name of Thai kingdom since Ayuthaya Period. It commonly appear in many western book, manuscript etc. However, in the period of Rama V, The concept of national state that’s influenced by western were adopted by Thai king and Siam become a name of a nation in South East Asia.

In Chinese Archives called Siam by using a word "เสี่ยมล้อ" (暹羅) [Xiānluó] since Sukhothai Period. Some evidence indicate the Siam word is from 2 words, “xian” is from the name of Sukhothai kingdom, luo is from the name of Lavo kingdom (later, Ayuthaya kingdom). So China is a first nation that using the word “Siam” for call a south kingdom. From this evidence, It is assumed that Siam is a name that Chinese call a south nation, then western country use this name for call Thailand.

Thailand is a name of current Siam, Although the name was changed on 24 June 1939 , At the time Thailand was in a period of Nationalism (Fascism) that led by Plaek Phibunsongkhram.

“Using word Siam is not appropriate for our national ethnic (Thai), In future foreigner that live in our country maybe claim Siam as own country. We are Thai we are living in Siam, Chinese also live in Siam, If migration of foreigner increase in thousands years, we will not understand what is Siam, who was own of Siam? ”

- Plaek have said about the using Thailand instead of Siam in Parliament 1939.

In fact, English name of Thailand was changed back to Siam again, and nationality of Siam also was changed to Siamese in a short period of Pridi Banomyong in 1946 - 1949. In 1949 Plaek Phibunsongkhram was elected to the government, So he changed the nation name back to Thailand/Thai again.

By the way, before 1946 Thai was also used for name of nation in the same way with Siam without separation.

In term of use, word Siam still in use for literature and poem. or about royalty such as Sayamminthr (สยามมินทร์; lit;leader of Siam)

In my opinion, Siam/Siamese is a best word to refer to current Thailand because Thai is a majority ethnic, but Thailand is not only Thai living. However Thailand racial conflict is not a problem. Everyone thought they are Thai, although they are Chinese or minorities.