The political doctrine or belief system that the civil government should have supreme authority over religious institutions and matters.
From Thomas Erastus (16th-century theologian) + '-ism' (suffix creating abstract nouns for doctrines or belief systems). The term emerged in 17th-century English political discourse to describe state supremacy over the church.
Erastianism became a major flashpoint in 17th-century England—Cromwell's government and later politics revolved around the question of whether Parliament or the Church of England should really be in charge, and 'Erastianism' became the label for the state-power side of that argument!
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