How many crusades were there over the course of 200 years ago?

What did the Romans call yeast? Who was the emperor during the Fall of Rome? Who is said to have first coined the term? How did the crusades affect monarchs and popes? What state has its legal system based on roman civil law format? What is the difference between gold mining now and when it was the gold rush? Who developed dbms? What negatives happened as a result of the crusades? Why was the Russian civil war important? What year was it four centuries ago? The ancient Greeks developed the first mathematical system of perspective but this knowledge was lost in the West after the fall of the Roman Empire. During what period was perspective rediscovered in? What affects did technology have on civilization? What are the four parts of the manor system? As described i the article what did the iron curtain symbolize? How did the ideas of Copernicus Kepler Galileo and newton change European world view? Why were westerens worried in 1802? What technilogical advances happened between 1950 - 2004? Where does the last name Whitney come from? How many years has it been since 1844? Why were the vikings so problematic for western Europe?