The Engagers were divided into four "Classes," who were rendered incapable by "The Act of Classes" of holding any office, civil or military.

This Act deprived the country of the services of thousands of men, just at the moment when the English army, the Independents, Argyll's allies, were holding the Trial of Charles I.; and, in defiance of timid remonstrances from the Scottish Commissioners in England, cut off "that comely head" (January 30, 1649), which meant war with Scotland.
SCOTLAND AND CHARLES II.
This was certain, for, on February 5, on the news of the deed done at Whitehall, the Estates proclaimed Charles II.

as Scottish King--if he took the Covenant.

By an ingenious intrigue Argyll allowed Lauderdale and Lanark, whom the Estates had intended to arrest, to escape to Holland, where Charles was residing, and their business was to bring that uncovenanted prince to sign the Covenant, and to overcome the influence of Montrose, who, with Clarendon, of course resisted such a trebly dishonourable act of perjured hypocrisy.

During the whole struggle, since Montrose took the king's side, he had been thwarted by the Hamiltons.