Fa Ngum ya sake jagorantar Lan Xang zuwa yaki a cikin 1360s da Sukhothai , inda Lan Xang ya yi nasara wajen kare yankinsu amma ya ba ƙungiyoyin kotunan da ke fafatawa da jama'ar da suka gaji da yaƙi ya ba da hujjar korar Fa Ngum don goyon bayan ɗansa Oun Huean.A cikin 1371, Oun Huean ya sami sarauta a matsayin Sarki Samsenthai (Sarkin 300,000 Tai) sunan da aka zaɓa a hankali don yariman Lao-Khmer, wanda ya nuna fifiko ga al'ummar Lao-tai da ya yi mulki a kan ƙungiyoyin Khmer a kotu.Samenthai ya ƙarfafa nasarorin mahaifinsa, kuma ya yi yaƙi daLanna a Chiang Saen a cikin 1390s.A cikin 1402 ya sami karbuwa a hukumance ga Lan Xang daga Daular Ming a kasar Sin.^[22] A cikin 1416, yana da shekaru sittin, Samsenthai ya mutu kuma waƙarsa Lan Kham Daeng ta gaje shi.Tarihi na Viet ya rubuta cewa a lokacin mulkin Lan Kham Daeng a cikin 1421 tashin hankali na Lam Sơn ya faru a ƙarƙashin Lê Lợi a kan Ming, kuma ya nemi taimakon Lan Xang.An aike da dakaru 30,000 tare da sojojin dokin giwaye 100, amma a maimakon haka sun goyi bayan Sinawa.^[23]