Because there are countries, religions and nations. Because there's ego. You can't begin war if you feel one with the whole world. If you can't see differences and separateness between yourself and others, between your religion and other religions, between your nation and other nations, you are in peace.

"We look forward to the time when the Power of Love will replace the Love of Power. Then will our world know the blessings of peace." William Ewart Gladstone

"Peace of Mind brings Peace on Earth?" - Yes, but only if we recognise how the ego is the cause of all the wars inside the human mind and, by implication, also of all the wars in the world-at-large." Michael Hollingshead "The Man Who Turned on the World"