They lived in the Americas since they crossed the land bridge in the time of Pangea and lived in harmony with the Earth. Little did they know that their entire existence would be changed and threatened by the arrival of strangers. The Aztecs had made advances in agriculture and architecture, but they did not have large animals such as workhorses or a wheel. When Cortes arrived with the horses, this could have given them the opportunity to develop further. Native Americans in present-day America used the horse to hunt and be nomadic. Without the explorers who introduced these animals, Native Americans may never have been able to advance or acquire the culture they have today. One negative effect of the exploration was that the explorers were very cruel to the Native Americans. Many took their gold, brought diseases, fought with them, forced them to accept European customs and began the encomienda. These actions have caused their population to decline rapidly. They have no immunity to diseases such as smallpox and plague, along with people dying in battle or from exhaustion during slavery leaving very small numbers. This led to the death of entire tribes along with their unique language and culture. History is missing entire past societies that first lived in the Americas because explorers found them and killed them. The surviving Native Americans were treated poorly; some had to convert to Christianity and then begin following a modified European