What were three positive and three negative effects of European contact on Native Americans?

It can be showned by the "Colombian Exchange." This is the exchange of the crops, animals and resources that went between the New and Old World.

From the Americas came peppers, maize, potatoes, tomatoes, snap beans, lima, beans, and squash. Maize and potatoes became staple crops throughout Europe. So much so that the Irish potato crop failed, the result was famine.

From Europe, to the Americas came wheat, rye, barley, oats and millet. The first two crops are used in bread, a mainstay today.

The horse was a European import. When adopted by the Native Americans, the result was the Great Plains cultures.

The Americans produced vast amounts of gold and silver. However the material was obtained, the amount imported to Europe made economies based on money possible. This allowed more trade.

Having somewhere to go and new opportunities invigorated Europe. People could now seek their fortune or get a fresh start. Having a destination also increased technological development of deep ocean ships.

There is a dark side to the exchange. When Europeans first came to the Americas they inadvertently introduced a number of diseases. These included forms of Tuberculosis, measles, cholera, typhus, and smallpox. Oh all the exchanges between the Native Americans and the Europeans, disease had the most impact. Remember the germ theory and knowledge of the spread of disease was centuries in the future

Native Americans had little immunity to any of these imported diseases. The migration route into the Americas had been through arctic regions. The cold acted as a "filter" preventing some diseases from entering. During their thousands of years of isolation, the inhabitants of the Americas had avoided the disease that swept through the rest of the world. However, this also meant that they had no immunity, protection from these same illnesses.

As a result, fully half the population became ill when exposed to smallpox. Worse, they often contracted the diseases most virulent form, variol major. This form is hemorrhagic and attacks the heart, lungs and liver. Similar infection rates were found with the other imported diseases.

While the diseases weren't spread as a deliberate policy or as a form of germ warfare there are recorded instances where deliberate attempts were made to spread the disease. During Pontiac's Rebellion in 1763, Lord Amherst is recorded as trying to spread smallpox through infected blankets.

Europeans knew to avoid contact with those that were sick and had some ideas of how illness spread. However, they neither knew about germs or how susceptible Native Americans were to disease. As example, it wasn't until 1796 that an effective vaccination for smallpox was developed. Using smallpox as a germ warfare weapon could backfire.

One estimate is that 90% of the population decrease after 1492 was due to disease. Another estimate puts the death by disease at 3,500,000 Native Americans