Why did the population of Native Americans decline drastically?

Answer 1

The Native Americans were killed off by American settlers in a number of different ways. For a few examples:

• Christopher Columbus' first act on meeting a native was to run him through with a sword to "show his power" (from his own diary). Columbus was later convicted of personally murdering 300,000 men women and children, and ordering the murder of another 700,000 - barbarous acts (quoting the court). He was later pardoned by the King of Italy.
• American Settlers lured approximately 250 Pamunkey tribesmen to a "Peace Talk" where they were given poisoned wine, those that did not drink the wine were strangled by hand.
• American Settlers set fire to a fortified Pequot village and shot anyone who tried to escape, killed were: 700 old people, women and children - most men were on hunting parties at the time.
• The tactic used above was so successful it was used again in New York by John Underhill; burning a village at night killing approximately 500.
• The Pennsylvania Militia, because it was low on gunpowder (bullets), took 96 men women and children into a shed and smashed their heads with a mallet - only 2 children escaped. Followup reports showed that some women were killed still clutching new born babies to them, the babies had their skulls crushed too.
• On June 24, 1763, William Trent, a local trader, recorded in his journal that two Indian chiefs had visited the fort, urging the British to abandon the fight, but the British refused. Instead, when the Indians were ready to leave, Trent wrote: "Out of our regard for them, we gave them two Blankets and an Handkerchief out of the Small Pox Hospital. I hope it will have the desired effect." There are at least two other recorded incidents of American Settlers intentionally spreading small pox to the natives.
• In California Americans paid money to ride in a train car and shoot indians, who were driven near the tracks to be shot.
• The Texas Rangers were founded for the single purpose of a "Scorched Earth Policy" to drive the Indians out of Texas. It is well documented that the Texas Rangers killed men, women and children without reserve; burnt whole villages and crops.

It is also interesting to note that the amount of Native American's killed is directly proportional to the number of American Colonists with guns, to kill them.

Answer 2

There were many causes, but one of the earliest and most significant were the Infectious Diseases from Europe that they had no resistance to (e.g. smallpox, measles, chickenpox, cholera, typhus, whooping cough).

Answer 3

Small pox, flu, ethnic cleansing