As of 2009, the largest and most widespread religion in the world was

Christianity, I believe, is the largest and most widespread religion of the world as of 2009.

Yes, it is Christianity.

Christianity is the world's biggest religion, approximately 2.9 billion followers are acknowledged being Christians. Christians understand that Jesus is the Messiah and God's only given son, thoroughly immaculate and thoroughly rational, also the guardian of mankind. According to the scripture, Christ is coming in the last day, that is rapture, to take all who believes in him! ^-^

Nation of conflicting ethnic groups