A cikin 1548 Sarki Sethathirat (a matsayin SarkinLanna ) ya ɗauki Chiang Saen a matsayin babban birninsa.Har yanzu Chiang Mai yana da ƙungiyoyi masu ƙarfi a kotu, kuma barazanar Burma da Ayutthaya suna ƙaruwa.Bayan mutuwar mahaifinsa, Sarki Sethathirath ya bar Lanna ya bar matarsa ​​​​a matsayin mai mulki.Lokacin da ya isa Lan Xang, an nada Setthathirath a matsayin Sarkin Lan Xang.Tafiyar ta karfafa bangarorin da ke hamayya da juna a kotu, wadanda a shekara ta 1551 suka nada Chao Mekuti a matsayin sarkin Lanna.^{[36 <>]} A shekara ta 1553 Sarki Setthathirat ya aika da sojoji su kwato Lanna amma aka ci nasara.Haka kuma a cikin 1555 Sarki Setthathirat ya aika da sojoji su kwato Lanna bisa umarnin Sen Soulintha, kuma sun yi nasarar daukar Chiang Saen.A cikin 1556 Burma, karkashin Sarki Bayinnaung ya mamaye Lanna.Sarki Mekuti na Lanna ya mika wuya ga Chiang Mai ba tare da fada ba, amma an maido da shi a matsayin basaraken Burma a karkashin mamayar sojoji.^[37]A cikin 1560, Sarki Setthathirath ya ƙaura daga Luang Prabang zuwa Vientiane babban birnin Lan Xang a hukumance, wanda zai kasance babban birnin cikin shekaru ɗari biyu da hamsin masu zuwa.^[38] Babban motsi na babban birnin ya biyo bayan wani shirin gine-gine mai fa'ida wanda ya haɗa da ƙarfafa tsaro na birni, gina babban gidan sarauta da Haw Phra Kaew don gina Emerald Buddha, da manyan gyare-gyare ga That Luang a Vientiane.Burma sun juya arewa don su kori Mekuti na Lanna, wanda ya kasa goyon bayan mamayewar Burma na Ayutthaya a 1563. Lokacin da Chiang Mai ya fada hannun Burma, wasu 'yan gudun hijira sun gudu zuwa Vientiane da Lan Xang.Sarki Setthathirath, da ya gane cewa ba za a iya riƙe Vientiane a yaƙi da dogon lokaci ba, ya ba da umarnin a kwashe birnin kuma a kwashe kayayyaki.Lokacin da Burma suka kai Vientiane an tilasta musu shiga cikin karkara don samun kayayyaki, inda sarki Setthathirath ya shirya hare-haren ’yan daba da kananan hare-hare don muzgunawa sojojin Burma.Fuskantar cututtuka, rashin abinci mai gina jiki da yaƙin neman zaɓe, an tilastawa sarki Bayinnaung ja da baya a shekara ta 1565 ya bar Lan Xang ɗaya tilo da ta rage mai cin gashin kanta ta Tai.^[39]