Why did the Navajo long walk happen?

The larger answer is: The Long Walk was part of the larger effort by the US government to remove all the native peoples from their lands in order to take them for settlers use and for the resources on them.

The Navajo answer might be: as in the previous worlds that they emerged from, fighting in this world led to becoming no longer in a state of hózhǫ́. This led to disaster.

The proximate answer is: After Narbona was killed in 1849 the Navajo came into conflict more and more with the new American government and settlers who had come with the end of the Mexican American war. The American army established forts in Navajo lands, something the Mexicans and Spanish had not done. They tried to reduce Navajo lands with the treaty of 1858 and a pro Navajo Indian agent was reassigned to West Point at that time.

William T. H. Brooks of the U.S. Army began a destructive cycle of raids and counter-raids with the Navajo culminating in the near-sacking of Fort Defiance by approximately 1,000 Navajo warriors under the leadership of Manuelito and Barboncito on April 30, 1860.

Colonel Manuel Chaves, commander of Fort Wingate had 30 Navajo killed in a dispute over a horse race. After that plans for the Long Walk began by General James H. Carleton. The Bosque Redondo "reservation" or internment camp was established on October 31, 1862 by Congress.

But it probably would not have happened if then the Civil War was coming to New Mexico. This brought Carleton into power in New Mexico and he instituted his plan once the Rebels in New Mexico had been easily defeated and there was little else for his command to do.

Some people think:

"I think that will depend upon who you ask. Two things comes to mind surrounding this event with the Navajo and the current dominant culture: first, invading Europeans firmly believed in "Manifest Destiny" and for the Navajo it was the beginning of the effects of spiritual disconnectedness from Diety."