In 1904, Chile and Bolivia signed the Treaty of Peace and Friendship that resulted from the War of the Pacific, which ended in 1883. Chile beat Bolivia, and Bolivia, which until then had a Pacific coastline, lost it and became the landlocked nation you know and often immediately forget about today. (Peru was also involved. Chile took some coastline from them too.)
The International Court of Justice has been officially informed that Bolivia would like that coastline back. Bolivia always has wanted it back; it never got rid of its navy, though now it just patrols lakes and rivers. Chile's reaction has been to openly laugh it off on the grounds that, dude, we've been under this treaty for how long now and we're just supposed to hand the land back?
That is about the reaction you ought to have too. Bolivia's chances of pulling this off are about the same as the Marlins selling out the rest of the season. In fact, if they reclaimed the coastline they had before the war- a portion that includes the city of Antofagasta- it would split Chile and the northernmost section (containing Arica and Iquique) would become an exclave. But it's worth at least noting that they've filed it.