To try to understand why and how so many different denominations developed, let's take a very brief look at the history of the church:
After Jesus died, Simon Peter, one of Jesus' disciples, became a strong leader in the Jewish Christian movement. Later James, most likely Jesus' brother, took over leadership. These followers of Christ viewed themselves as a reform movement within Judaism yet they continued to follow many of the Jewish laws.
At this time Saul, originally one of the strongest persecutors of the early Jewish Christians, had a blinding vision of Jesus Christ on the road to Damascus, and became a Christian. Adopting the name Paul, he became the greatest evangelist of the early Christian church. Paul's ministry, also called Pauline Christianity, was directed mainly to Gentiles rather than Jews. In subtle ways, the early church was already becoming divided.
Assemblies of God
United Church of Christ
Comparison Charts of Christian Denomination