This study is concerned with ethnic identities and, social space opening, as well as with those changes in the ethnic identity of socially marginalized ethnic groups, along with relationships between the nation state and local communities. The research methodology was based on a multi-field descriptive ethnological approach, andthe study focused on areas with continuously moving and changing power interactions and operations. There have been regions with perpetual movements of people, goods, and transnational cultures. Each study area has its own unique context and conditions such as border areas of Chiang Khong, Chiang Saen, Tha Song Yang, Mae Ai, Fang and Pang Ma Pha, as well as non-border areas of Night Bazaar or Doi Pui Hmong Village, respectively. The research findings revealed that borders have been areas of cultural and power conflicts due to a unilateral nation-state building process according to the conventional nationalism of the Thai state,which has spread its power to border areas. This spread of power has encountered challenges due to the diversity of cultures and ethnic identities along borderlines. Therefore, an ethnic identity is not a fixed pattern, but “a strategy” for presenting oneself according to circumstantial changes and interests. Furthermore, an ethnic identity is an issue of negotiation and contestation by dismantling one’s ethnic boundary or fence that separates one individual, or a group, from other groups and the state in an attempt to prevent and modify elements of confrontation among people of various groups. The perpetual dismantling and rebuilding of an‘ethnic fence’ have brought about reformation, reproduction, and redefinition of the structure of power at the border, which is flexible and supple according to the context of negotiations and prevailing conditions.