The invention that had the greatest impact on western expansion was the repeating rifle. Before the repeating rifle, settlers and explorers had to reload their guns after every shot, which was a slow and cumbersome process. The repeating rifle allowed them to fire multiple shots in quick succession, which gave them a significant advantage over Native American tribes who were still using single-shot weapons. The repeating rifle also made it easier for settlers to hunt for food and defend themselves against attacks from wild animals.