A cikin 1917 Siam ya shelanta yaki a kan Daular Jamus da Ostiriya-Hungary, musamman don samun tagomashi tare da Burtaniya da Faransanci .Shigar da alamar Siam a yakin duniya na daya ya ba ta damar zama a taron zaman lafiya na Versailles, kuma ministan harkokin wajen kasar Devawongse ya yi amfani da wannan damar wajen yin muhawara kan soke yarjejeniyoyin da ba su daidaita ba a karni na 19 da kuma maido da cikakken ikon mallakar Siamese.Amurka ta wajabta a 1920, yayin da Faransa da Biritaniya suka biyo baya a 1925. Wannan nasara ta sami ɗan farin jini ga sarki, amma ba da daɗewa ba ta yi nasara saboda rashin gamsuwa da wasu batutuwa, kamar almubazzaranci da ya yi, wanda ya zama sananne a lokacin da koma bayan tattalin arziki na Siam. a 1919. Akwai kuma cewa sarki ba shi da ɗa.Babu shakka ya fifita haduwar maza fiye da mata (al’amarin da shi kansa bai damu da ra’ayin Siyama ba, amma kuma ya kawo cikas ga zaman lafiyar masarautar saboda rashin magada).A ƙarshen yaƙi, Siam ya zama memba na Ƙungiyar Ƙungiyoyin Ƙasashen Duniya.A shekara ta 1925, Amurka, Birtaniya, da Faransa sun yi watsi da yancinsu na ketare a Siam.