What was the purpose of the reconstruction admendments?

These amendments were intended to guarantee freedom to former slaves and to establish and prevent discrimination in certain civil rights to former slaves and all citizens of the United States. The promise of these amendments was eroded by state laws and federal court decisions throughout the late 19th century.

a. because the u.s. was the leading with the most technology, economy, etc. also was teamed with other allies witch boosted the economy and materials to improve technology and use it.

nothing certain is known about what happened, but it seems that the country declined gradually, perhaps due to bad government, or, more likely, due to a series of bad harvests, which resulted in widespread and recurrent famine.