Good modern answer.:) Or if we want a historical one:September 11, 2001.
Muhammad's agenda was religious for the fist 10 years of his agenda. He failed. His own people saw right through him and called him a liar, a soothsayer (Devil worshiper) and a charleton, and they knew he was plagerizing his words from other religions. They called him out. He changed his agend from religious to political and declared war on all man kind with the pledge of accabah, and ordered his followers to do the same. The instant muhammad utterd quran 8:7, Kill every unbeliever. Wipe them out to the last, and if you're a follower of the quran, then that's when being an adherent of islam became a crime.
So to answer the question, over 1400 years ago.