Deterrence and diplomacy have been the fundamental tenets of Singapore's military defence policy. Through the years, the military has developed extensive links with armed forces from other countries. In recent years, there has also been an increased emphasis on international peace-keeping and relief operations, notably the peace-keeping operations in East Timor and the Persian Gulf and disaster relief in the Indian Ocean earthquake-tsunami of 2004, 2005 Nias earthquake and 2006 Yogyakarta earthquake in Central Java, Indonesia.