What is "landmarkism"

Landmarkism is a type of Baptist ecclesiology developed in the American South in the mid-19th century. It is committed to a strong version of the perpetuity theory of Baptist origins, attributing an unbroken continuity and unique legitimacy to the Baptist movement since the apostolic period. It includes belief in the exclusive validity of Baptist churches and invalidity of non-Baptist liturgical forms and practices. It led to intense debates and splits in the white Baptist community.