agree terms, but the English Parliament was concerned this would lead to the imposition of an absolutist structure similar to that of Scotland. James was forced to withdraw his proposals, and attempts to revive it in 1610 were met with hostility. Instead, he set about creating a unified Church of Scotland and England, as the first step towards a centralised, Unionist state. However, despite both being nominally Episcopal in structure, the two were very different in doctrine; the Church of Scotland, or kirk, was Calvinist in doctrine, and viewed many Church of England practices as little better than Catholicism. As a result, attempts to impose religious policy by James and his son Charles I ultimately led to the 1639–1651 Wars of the Three Kingdoms. The 1639–1640 Bishops' Wars confirmed the primacy of the kirk, and established a Covenanter government in Scotland. The Scots remained neutral when the First English Civil War began in 1642, before becoming concerned at the impact on Scotland of a Royalist victory. Presbyterian leaders like Argyll viewed union as a way to ensure free trade between England and Scotland, and preserve a Presbyterian kirk. Under the 1643 Solemn League and Covenant, the Covenanters agreed to provide military support for the English Parliament, in return for religious union. Although the treaty referred repeatedly to 'union' between England, Scotland, and Ireland, political union had little support outside the Kirk Party. Even religious union was opposed by the Episcopalian majority in the Church of England, and Independents like Oliver Cromwell, who dominated the New Model Army. The Scots and English Presbyterians were political conservatives, who increasingly viewed the Independents, and associated radical groups like the Levellers, as a bigger threat than the Royalists. Both Royalists and Presbyterians agreed monarchy was divinely ordered, but disagreed on the nature and extent of Royal authority over the church. When Charles I surrendered in 1646, they allied with their former enemies to restore him to the English throne. After defeat in the 1647–1648 Second English Civil War, Scotland was occupied by English troops which were withdrawn once the so-called Engagers whom Cromwell held responsible for the war had been replaced by the Kirk Party. In December 1648, Pride's Purge confirmed Cromwell's political control in England by removing Presbyterian MPs from Parliament, and executing Charles in January 1649. Seeing this as sacrilege, the Kirk Party proclaimed Charles II King of Scotland and Great Britain,