The scope and purpose of the principle of self-determination has evolved significantly in the 20th century. In the early 1900’s, international support grew for the right of all people to self-determination. This led to successful secessionist movements during and after WWI, WWII and laid the groundwork for decolonization in the 1960s.
Contemporary notions of self-determination usually distinguish between “internal” and “external” self-determination, suggesting that "self-determination" exists on a spectrum. Internal self-determination may refer to various political and social rights; by contrast,external self-determination refers to full legal independence/secession for the given 'people' from the larger politico-legal state. http://www.law.cornell.edu/wex/self_determination_international_law
uti possidetis juris, requiring the maintenance of the territorial status quo to preserve stability, order and traditional legal boundaries (and hence possibly conflicting with principle of self-determination) (Burkina Faso/Mali, ¶¶25-26, pp.16-17 ("At first sight this principle [UPJ] conflicts outright with another one, the right of peoples to self-determination.")