Which era is credited with causing such changes as improving workplace conditions, food safety, housing standards, and passage of the sixteenth, seventeenth, eighteenth, and nineteenth amendments?

The Progressive Era

Explanation:

The Progressive Era was a period of widespread social activism and political reform. This took place from the 1890s to the 1920s. The Progressive Era led to major improvements in various social problems, such as industrialization, urbanization, immigration, and political corruption. It saw the passage of several amendments to the Constitution and the regulation of monopolies and corporations.

1. it was caused by feudalism

2. charlemagne used christianity as a major cornerstone for his rule. cloisters were built all over the empire to act as centers for the (re)population of the vast european wilderness.

3. the europeans feared the next raid every time chetak

i'm not so sure about #6. but i hope i you with the first 3.