Sunnis, Shi'ite have come after, Sunnis are the most main.
Shia Muslims believe shia Islam started from time of prophet and prophet many times used the term "shia of Ali" and many times said to Ali "you and your shia ..."
for example shia Muslims refer to such Hadithes (sayings of prophet):
"O Ali, you the first who enters Heaven and your shias are in chairs of light and they are happy and their faces are lumine around me. ask God forgive their mistakes and they will be my neighbors in Heaven.
انت اول داخل الجنة من امتی وان شیعتک علی منابر من نور مسرورون مبیضة وجوههم حولی ,اشفع لهم فیکونون غدا فی الجنة جیرانی
this saying is mentioned in many sunni books like these 2 book:
کفایة الطالب، ص135، و در مجمع الزواید ج 9 ص 131
Shia Muslims believe shia Islam is the original Islam of prophet and sunnism started when Abubakr selected by people and not by God and the will of God about Ali did not happen after prophet.