The United Nations Protection Force, Unprofor, was initially established in Croatia, with a mandate to safeguard UN "protected areas" from armed attack.
When civil war broke out between Serbs, Muslims and Croats in Bosnia, the world was slow to act. Unprofor's mandate was extended to ensure security at Sarajevo airport and the delivery of humanitarian aid in June 1992.
But Bosnia's request for UN monitors on its borders with Serbia was turned down, because there was no precedent for "pre-emptive" peacekeeping.
Unprofor peacekeepers had limited firepower and a weak mandate, which made it difficult for them to protect Bosnia's civilian population.
In the summer of 1995, lightly-armed peacekeepers stood by powerless as Serb forces killed thousands of men in Srebrenica, which they had been told was a "safe haven".