Multiculturalism was once the dream of many countries around the world, encouraging ethnically diverse cultures to live side by side in harmony. But critics say that dream has failed: that too many communities live separately - pursuing segregation rather than integration, fuelling dangerous resentment. Can you have a multi-racial, multi-faith society, without forcing people of different cultures to assimilate? Global Questions travels to Sydney, Australia - a young country built on immigration, where many cultures now live together - hailed by its former Prime Minister as the most successful multi-cultural society in the world. But even here there are real tensions, and the world recoiled in revulsion when a self-avowed Australian racist and white supremacist massacred fifty Muslims in Christchurch, New Zealand. So in this mobile, globalised world, is multiculturalism failing, and if so, what needs to replace it?