What started the 1540 Tiguex War in what is now the Albuquerque area was what ended the Battle of Glorieta during the Civil War - butchery of innocent equines.
At Glorieta Union soldiers snuck to Confederate supply wagons and killed all the mules. In the fields along the Rio Grande the Tiguex killed the Spaniards' mules and horses.
They were the first the Tiguex had ever seen. The superiority afforded the Spanish mounted on the new beasts played into the massacre no doubt, as did the horses' offense of being allowed by their Spanish masters to graze and trample Tiguex fields that terrible winter. The horses were priceless to the Spanish and no doubt highly trained, carefully bred and valued above nearly all else.
It was a turn-key event. Sad to imagine but no less part of the history that "started badly and stayed that way a long time."