Patrick Henry's opening remarks help us understand what the previous speakers had said that day in 1775:
"MR. PRESIDENT: No man thinks more highly than I do of the patriotism, as well as abilities, of the very worthy gentlemen who have just addressed the House. But different men often see the same subject in different lights; and, therefore, I hope it will not be thought disrespectful to those gentlemen if, entertaining as I do, opinions of a character very opposite to theirs, I shall speak forth my sentiments freely, and without reserve."
Henry went on at length to disparage the idea that further civil negotiation with Britain was likely to produce anything substantive in terms of benefiting the colonies. His speech was a rousing call-to-arms. Henry believed that the only option left to the colonies by March of 1775 was to gather the colonies and their militias together to form an army to remove Britain's army and navy from the American colonies.
The "unthinkable alternative to war" was, as he put it, was for the colonies to accept and endure "submission and slavery." Near the end of the speech Henry says, "gentlemen may cry Peace, Peace, but there is no peace." The gentlemen to whom he refers may be the previous speakers or just men who still believed that diplomacy could bring the colonies the relief they sought.
Henry spelled out what had not worked: petitions, remonstrances, and supplications. These specifics seem to be a response to the tactics that his opposition supported.