Answer :
Many people died and killed themselves, leaving the population low
Black death was one of the most dangerous epidemic in human history which occured in 14th century Europe. It's believed that its primary cause was the Yersinia pestis bactery. The plague started in China, then it moved to Crimea in about 1346, and then the bactery was probably spreaded throughout Mediterranean Sea by fleas on rats travelling on trading ships. Black death disease decreased population in Europe by 30-60% and worldwide by 10-20%. It shocked religious, social and cultural life of that time. Many people blamed various groups for invoking the plague (i.e. Jews, monks, pilgrims, beggars, foreigners etc. what caused many oppressions. Also lepers had been often isolated and killed. The black death had also a great impact on the 14th century art. Europeans needed about 150 years to regain the previous population.