Final answer:
The bald eagle population declined due to habitat loss, pollution, and the use of the pesticide DDT, with the latter playing a critical role in their endangerment until its ban in 1972.
Step-by-step explanation:
The near-extinction of bald eagles in the United States by 1960 was primarily caused by habitat loss, pollution of fresh water, and contamination of primary producers. These factors led to a significant decrease in the bald eagle population, from an estimated 500,000 in the 1700s to around 1,000 by 1960. It was the widespread use of the pesticide DDT that was particularly devastating to the bald eagle, leading to its classification as endangered in 1967. The eventual ban on DDT in 1972 is credited with helping the recovery of bald eagle populations, demonstrating the impact of human interaction and environmental policies on wildlife conservation.