Manifest Destiny is the belief that they have the duty to expand from coast to coast. One of the main inventions that helped them in this journey was to have a railroad that went from coast to coast. They named this railroad, the Transcontinental Railroad. This allowed for people to travel back and forth a lot faster. Another great invention was the telegraph, that allowed messages to be sent back and forth. These inventions made manifest destiny possible. Without them, it would be impossible. The US gained the following territories as a part of the Treaty of Guadalupe Hidalgo; California, Nevada, Utah, and Arizona, the entire state of Texas that then included part of Kansas, Colorado,Wyoming, Oklahoma, and New Mexico.
This period in history was full of wars. The societies were not developed enough for them to be able to work together. They all felt that they had the right and the duty to expand and become more powerful. This then caused them to fight more with other countries to get what they want. It took them a long time to realize that fighting doesn't help one side. All it does is destroy both sides. The US had an advantage because they had a strong factory and manufacturing system that could provide them with whatever supplies that they needed. They also, by now, had a strong financial backing, this allowed them to be able to do what they needed to do.
The US policy on the Native Americans fluctuated throughout history. Although most of the time, the US pushed the Native Americans farther west. As the US expanded west, they pushed them farther west. They believed that they were superior to everyone else and they could do whatever they wanted to. They also believed that it was their destiny to move west, and since these people were in the way and did not contribute anything to them, they then needed to get out of the way.