I'd say:
The U.S. government violated many of the treaties it had negotiated with Native American tribes.
The U.S. government violated many of the treaties it had negotiated with Native American tribes.Gold miners, farmers, and cattle ranchers laid claim to Native American lands.
During westward expansion, Americans had the desire to head west in search of land to begin their new lives/jobs as miners, farmers, etc. However, in doing so, the U.S. government broke many treaties they had with the Native American tribes. The most heartbreaking incident is known as the "Trail of Tears" where they had to leave their homelands to travel to marked/designated Indian Territory near the Mississippi.