The agreement left parts of the communist and conservative branches of the AFPFL dissatisfied, sending the Red Flag Communists led by Thakin Soe underground and the conservatives into opposition. Aung San also succeeded in concluding an agreement with ethnic minorities for a unified Burma at the Panglong Conference on 12 February, celebrated since as 'Union Day'. Shortly after, rebellion broke out in the Arakan led by the veteran monk U Seinda, and it began to spread to other districts. The popularity of the AFPFL, dominated by Aung San and the socialists, was eventually confirmed when it won an overwhelming victory in the April 1947 constituent assembly elections.