Hate to piss on your parade with the truth...
but it wasn't the Americans who (allegedly) gave smallpox infected blankets to the Indians. In fact, the incident appears to have happened in 1763, 13 years before the Declaration of Independence. The person who allegedly did this was British, a guy named Lord Jeffery Amherst, the namesake of Amherst, MA and Amherst University.
Biological warfare is an ancient practice, with the first recorded incident happening in 1346 by the Tartar army during its siege of Kaffa. They catapulted plague infected bodies into the city to sicken the population.