Patrick Henry's speech to the Second Virginia Convention in Richmond, Virginia, on March 23, 1775, provides some clues as to why he believes a British attack is imminent.
Patrick Henry starts out his speech by warning his listeners that the time for civility and ceremony is over. He asserts his right to speak truthfully and clearly about the dangers facing the colonies; passionately, he begs his listeners not to be lulled into a dangerous sense of security by counterfeit British cordiality. Instead, Patrick Henry alerts his listeners to trust the evidence before their eyes:
Ask yourselves how this gracious reception of our petition comports with these war-like preparations which cover our waters and darken our land... Let us not deceive ourselves, sir. These are the implements of war and subjugation; the last arguments to which kings resort. I ask, gentlemen, sir, what means this martial array, if its purpose be not to force us to submission? Can gentlemen assign any other possible motive for it? Has Great Britain any enemy, in this quarter of the world, to call for all this accumulation of navies and armies? No, sir, she has none. They are meant for us; they can be meant for no other. They are sent over to bind and rivet upon us those chains which the British ministry have been so long forging.
He warns that the 'martial array' they see before their eyes represents the advance of an implacable enemy bent on subjugation, not peace. He further asserts that the colonists have engaged in every possible resolution to avoid war; the only thing they will not do is to surrender. If they will not act to protect their freedom and right to exist, Henry warns that the British will entirely vanquish them as a people.
Patrick Henry encourages his listeners not to despair:
The battle, sir, is not to the strong alone; it is to the vigilant, the active, the brave.
He ends his speech with the famous lines which have endured for generations:
I know not what course others may take; but as for me, give me liberty or give me death!