During the Reformation in the 16th Century, Henry VIII declared the Church of England independent of the Roman Catholic Church with himself as its head. It was the result of many factors, some political and some theological, but it has given rise to a distinct form of Christianity, known as Anglicanism.
The Episcopal Church is a member of the worldwide Anglican Communion, the churches around the world that trace their roots to the Church of England, and maintain a “communion” with it, hence the name “Anglican.” Other members of the Communion include the Anglican Church of Canada and the Anglican Church of Nigeria. In fact, most Anglicans now live in Africa.
The member churches of the Anglican Communion are joined together by choice in love, and have no direct authority over one another. The Archbishop of Canterbury, the head of the Church of England, is acknowledged as the spiritual head of the Anglican Communion, but while respected, the Archbishop does not have direct authority over any Anglican Church outside of England.
While there are other churches that call themselves “Anglican,” only one Church in any country can be considered “in full communion” with the Church of England, and the Episcopal Church is the American member of the Communion.