Final answer:
The United States didn't imperialize eastward in the 1860s and 1870s due to fear of attacks on their borders and the difficulties associated with maintaining empires. Opponents of imperialism also argued against it, citing examples of empires being associated with tyranny and oppression.
Step-by-step explanation:
The United States didn't imperialize eastward in the 1860s and 1870s due to several reasons. One reason was the fear of attacks on their borders. The acquisition of empire had shown the difficulty of maintaining empires, as seen in events like the Philippine Insurrection. Additionally, opponents argued against imperialism, citing past examples of empires being synonymous with tyranny and oppression.