premise: The United Nations is leading international efforts to build a bi- zonal, bi-communal federation in Cyprus.
  The island has been divided since 1974 when Turkish mainland troops invaded the northern third of Cyprus in the wake of a coup in Nicosia backed by the right-wing junta then ruling Greece.
  Western diplomats said that Annan would have the difficult task of finding a replacement for Han who is familiar with the issues while being acceptable to both the Greek- and Turkish-Cypriot communities.
  And in the light of ethnic unrest which has hit the island since last summer, "things could be disrupted" along the road to a summit, one diplomat said.
  The five permanent members of the UN Security Council -- Britain, China, France, Russia and the United States -- are expected to discuss Cyprus at Russia's suggestion later this month.
   What could happen due to the ethnic unrest that has hit the island last summer?
hypothesis: Turkish mainland troops invaded the northern third of Cyprus