John Murray, 4th Earl of Dunmore, originally from Scotland, was the royal governor of the Colony of Virginia from 1771 to 1775. During his tenure, he worked proactively to extend Virginia's western borders past the Appalachian Mountains, despite the British Royal Proclamation of 1763. He notably defeated the Shawnee nation in Dunmore's War, gaining land south of the Ohio River. As a widespread dislike for the British crown (as a result of the American Revolution) became apparent, however, Dunmore changed his attitude towards the colonists; he became frustrated with the lack of respect towards the British Crown. Dunmore's popularity worsened after, following orders, he attempted to prevent the election of representatives to the Second Continental Congress.
On April 21, 1775, he seized colonial ammunition stores, an action that resulted in the formation of an angry mob. The colonists argued that the ammunition belonged to them, not to the British Crown. That night, Dunmore angrily swore, "I have once fought for the Virginians and by God, I will let them see that I can fight against them." This was one of the first instances that Dunmore overtly threatened to institute martial law. While he had not formally passed any rulings, news of his plan spread through the colony rapidly. A group of slaves offered their services to the royal governor not long after April 21. Though he ordered them away, the colonial slaveholders remained suspicious of his intentions.
As colonial protests became violent, Dunmore fled the Governor's Palace in Williamsburg and took refuge aboard the frigate HMS Fowey at Yorktown on June 8, 1775. For several months, Dunmore replenished his forces and supplies by conducting raids and inviting slaves to join him. When Virginia's House of Burgesses decided that Dunmore's departure indicated his resignation, he drafted the formal proclamation, signing it on Nov 7. It was publicly proclaimed a week later.