Final answer:
The Wounded Knee Massacre in December 1890 is significant for marking the end of the Indian Wars and symbolizing the end of an era on the Great Plains. It preluded shifts in American foreign policy towards imperialism and coincided with the closure of the Populist movement, influenced by the Klondike Gold Rush and the Spanish-American War.
Step-by-step explanation:
The significant event often regarded as signaling the end of an era on the Great Plains took place in December of 1890, known as the Wounded Knee Massacre. This tragic event marked the culmination of the U.S. government's efforts to subdue Native American tribes and represented a symbolic end to the Indian Wars. On December 29, 1890, U.S. Army troops opened fire on a camp of Lakota Sioux at Wounded Knee Creek in South Dakota, killing many men, women, and children. This massacre is seen by many historians as a turning point, reflecting the profound changes on the Great Plains and the end of a way of life for Native Americans. The 1890s also marked a shift in American foreign policy, moving towards imperialism with events like the Spanish-American War of 1898, which further shifted the nation's focus away from domestic issues related to the West and Native American relations. Additionally, the economic upturn from the Klondike Gold Rush and the impetus of the impending Spanish-American War helped to close the chapter of the Populist movement of the late 19th century.