Historians cannot agree how much damage the attempt to spread smallpox at Fort Pitt caused. Historian Francis Jennings concluded that the attempt was "unquestionably successful and effective" and inflicted great damage to the Native Americans. Historian Michael McConnell writes that, "Ironically, British efforts to use pestilence as a weapon may not have been either necessary or particularly effective", noting that smallpox was already entering the territory by several means, and Native Americans were familiar with the disease and good at isolating the infected. Historians widely agree that smallpox devastated the Native American population. It is estimated that 400,000–500,000 (possibly up to 1.5 million) Native Americans died during and years after the Pontiac's War, mostly from smallpox,