The correct answer is better C.
Explanation: Frederick Jackson Turner was an American historian, known primarily for his work in the area of US history.
Answer:
Navigating hazardous rivers, the Corps of Discovery paddled the Clearwater to the Snake and on at last to the Columbia. Driven to reach the western sea before winter and challenged by treacherous white water, Lewis and Clark had little time to describe the dark-walled canyons and treeless plains around them.
Explanation:
The correct answer is <span>(2) inability to force back foreign invaders
Both empires had foreign enemies from beyond the borders who attacked them and raided their coasts and borders all the time which severely weakened the country since they constantly had to invest into the military and protecting borders and similar things and they started running out of money before they completely got destroyed.</span>