The main purpose of the Hartford Convention, which took place in 1814-1815, was primarily related to the grievances of the New England Federalists during the War of 1812. While it expressed concerns over the war and its impact on New England, particularly regarding trade restrictions and the federal government's policies, the most accurate option from your list would be:
2. to protest the war with Britain
The convention aimed to address issues arising from the war and the federal government's handling of it, although it did also involve discussions about strengthening the Federalist Party and advocating for New England's interests.