The migrations and missionary efforts of each of these groups lead to the widespread significance of the Westminster Assembly throughout the English-speaking world. The Assembly's Confession was particularly influential in American Protestant theology. It was included with congregationalist changes as part of the 1648 Cambridge Platform, a statement produced by ministers of colonial Massachusetts and the surrounding region, and again in colonial Connecticut as part of the 1708 Saybrook Platform. The Confession was modified for American Baptists in the 1707 Philadelphia Confession. The Adopting Act of 1729 required American Presbyterians to agree to the theology of the Assembly's Confession, and the Confession remains a part of the Presbyterian Church (USA)'s "Book of Confessions". The Confession has been called "by far the most influential doctrinal symbol in American Protestant history" by the historian of religion Sydney E. Ahlstrom.