It sounds like Koo Kum aka Sunset at Chaophraya. They didn't get married to stop the war though. They had to get married to get a bondage/trust between Thai and Japan. And at the end pra’ek dies.
There are different remakes of this storyline. I’m going to list them from oldest to recent, the ones I know. Koo Kum:
(Movie) Starring: Waruth Woratum and Jintara Sookkapat
(Tv-series) Starring: Bird Thongchai McIntyre and Kwang Kamolchanok
(Movie) Starring : Bird Thongchai McIntyre, Oum Appasiri Nitiphon, and Tui Thiraphat Sajakul
(Tv-series) Starring: Num Sornram and Benz Porchita
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