Four years before his death in 1791, John Wesley was concerned about his Methodist followers. "I still think that when the Methodists leave the church," he worried in 1787, "God will leave them."

When he started preaching in 1739, Wesley's only mission was to revive the Church of England, not start a new one. But on the family tree of American churches, several major branches find their roots in Wesley's 18th century movement.

Wesley's most direct descendants are the 10 million members of the United Methodist Church. That's not counting nearly 4 million members of churches like the African Methodist Episcopal Church, the 70 million members of the World Methodist Council or still millions more in the Salvation Army, the Wesleyan churches, the Church of the Nazarene or countless Holiness churches.

Add to that the 625 million Pentecostals around the world who claim Wesley as a spiritual forbear and you have the second largest Christian movement in the world, outpaced only by the Roman Catholic Church.

Now, 300 years after his birth (June 17, 1703), perhaps no one would be more surprised by Wesley's enduring influence -- and the host of churches he fathered -- than Wesley himself.

"Certainly he would be one of the three most influential Christian leaders as far as his effects on American religious life," said the Rev. Vinson Synan, dean of the School of Divinity at Regent University and author of The Century of the Holy Spirit: 100 Years of Pentecostal and Charismatic Renewal.

It's an ironic mantle to place on someone who spent only 18 months in the American Colonies, during a disastrous stint as a missionary to Georgia from 1735 to 1737.

Yet Wesley's theological DNA is still deeply imprinted on American religion, from Billy Graham revivals and the 41 percent of Americans who claim to be "born again" to the hospitals, universities and social movements that were founded to usher in Wesley's era of social holiness, even if we're not Protestant or not Wesleyan," said Brother Jeff Gros, who oversees ecumenical dialogue for the U.S. Conference of Catholic Bishops.

By the mid-1800s, fueled by frontier conversions, the Methodists were the largest Christian group in the United States. Methodists pioneered circuit riders and a sophisticated "class meeting" system that relied on lay leaders rather than ordained professionals. Wesley's gospel found particular appeal among the poor, illiterate and uneducated.

"The fact that Wesley didn't assume that what you were born into was what you had to be is really a new patent on religion that people take for granted today," said Martin Marty, the dean of American church historians, at the University of Chicago.

Methodists established a wide swath of territory from Baltimore to Kansas where they became the typical Protestant church. Along the way they started such educational institutions as Emory, Duke, Boston University and Northwestern while championing abolition, prohibition and eventually civil rights.