Which of the following was a feature of Polk's administration?

The focus on acquiring new territories was indeed a defining feature of President James K. Polk's administration. Polk, who served from 1845 to 1849, was a strong proponent of Manifest Destiny, the belief that it was the United States' destiny to expand its territory across the North American continent. This belief drove his administration to pursue several key territorial acquisitions.

Under Polk, the U.S. expanded significantly through the annexation of Texas, which was a contentious issue that eventually led to the Mexican-American War. Additionally, Polk oversaw the acquisition of Oregon Territory through diplomatic negotiations with Britain, further extending the U.S. borders to the Pacific Coast. The Mexican-American War resulted in substantial territorial gains as well, including present-day California, Arizona, New Mexico, Utah, Nevada, and parts of Colorado and Wyoming, solidifying Polk’s focus on territorial expansion as a hallmark of his presidency.

In contrast, aspects such as progressive taxation, significant tariff increases, and long-term diplomatic relations with Mexico do not align with the main objectives and actions taken during Polk's administration. His focus was primarily on expansion rather than reforming tax structures or establishing prolonged diplomatic relationships.