Bosnian Serb leader Milorad Dodik has defended his predecessor, Radovan Karadzic, against war crimes at his trial in The Hague.
Mr Dodik blamed Muslim ambition for an Islamic state as laying "the foundation for the future conflict in Bosnia".
More than 100,000 people died during the war from 1992-1995.
Mr Karadzic faces 10 charges of genocide and crimes against humanity during the war, including the siege of Sarajevo and the Srebrenica massacre.
The 67-year-old went on trial at the International Criminal Tribunal for the former Yugoslavia (ICTY) in October 2009, following his capture after almost 13 years on the run.
Mr Dodik is president of Bosnia's Serb-dominated Republika Srpska.
He accused the Muslims' war-time leader Alia Izetbegovic of seeking to create an Islamic state under Sharia law despite not having a majority in Bosnia in the months leading up to the outbreak of war.
"I recognised his activities at the time and how he was carrying out his political plan," Mr Dodik told the court. "It has elements of fanaticism."
He said Izetbegovic supporters armed Muslims before the conflict, and that the first victims of war were Serbs shot by Muslims.
Central to Mr Karadzic's defence is the argument that Serbs only resorted to military action to defend themselves from Muslim aggression during the collapse of the former Yugoslavia.
However, most allegations against Mr Karadzic at the ICTY involve Serbs persecuting and expelling Muslims and Croats.
More than 7,000 Bosniak (Bosnian Muslim) men and boys were killed at Srebrenica in the worst single atrocity in Europe since the end of World War II.
During the 44-month siege of Sarajevo more than 12,000 civilians died.