I want to know the answer to the following question:
By which decade had the KKK become very active in Detroit?
All the background I'm provided with is that "The Black Legion, a secret vigilante group, was active in the Detroit area in the 1930s, when one-third of its estimated 20,000 to 30,000 members in Michigan were based in the city.". Is that enough to answer the question?
Answer: no