FAA changes in testing standards

Please provide thoughtful and complete answers to the following questions:

Why did the Federal Administration Aviation (FAA) decide to change testing standards?

How did the Federal Aviation Administration (FAA) go about developing this change?

How does the Airman Certification Standards (ACS) differ from the Practical Test Standards (PTS)?

How will the Airman Certification Standards (ACS) impact flight training?

How is slow flight addressed differently by the Airman Certification Standards (ACS) compared to the Practical Test Standards (PTS)?