Black Death was one of the deadliest pandemics in human history (History of the world), peaking in Europe between 1348 and 1350. It is widely thought to have been an outbreak of bubonic plague caused by the bacterium Yersinia pestis, but this view has recently been challenged. Usually thought to have started in Central Asia, it had reached the Crimea by 1346 and from there, probably from black rats on merchant ships (Cargo ship), it spread throughout the Mediterranean (Mediterranean Basin) and Europe. The Black Death is estimated to have killed 30% to 60% of Europes population, reducing the worlds population from an estimated 450 million to between 350 and 375 million in 1400. This has been seen as creating a series of religious, social and economic upheavals which had profound effects on the course of European history. It took 150 years for Europes population to recover. The plague returned at various times, resulting in a larger number of deaths, until it left Europe in the 19th century.