After Siam extended its influence over Laos in the 18th and 19th centuries, the music of Laos began to spread into the Thai heartland. Forced population transfers from Laos into the newly acquired region of Isan and what is now Central Thailand accelerated the rapid adoption of "mor lam". Even King Mongkut's vice-king Pinklao became enamoured of it. But in 1857, following the vice-king's death, Mongkut banned public performances, citing the threat it posed to Thai culture and its alleged role in causing a drought. Performance of "mor lam" thereafter was a largely local affair, confined to events such as festivals in Isan and Laos. However, as Isan people began to migrate throughout the rest of the country, the music came with them. The first major "mor lam" performance of the 20th century in Bangkok took place at the Rajadamnern Stadium in 1946. Even then, the number of migrant workers from Isan was fairly small, and "mor lam" was paid little attention by the outside world.