There were several reasons for the decline in the population of Europe in the fourteenth century. One factor was the climate. There was a drop in temperature that is referred to as the Little Ice Age. With freezing winters and cooler and wetter summers, crops failed, which caused famine to occur. The change in climate led to a drop in population.

A second factor was the spread of the Black Plague. This disease arrived in Europe in 1347. It came when several trading ships arrived in Sicily. Many sailors were dead and others suffered from fever and the inability to eat foods without regurgitating them. The disease spread quickly, killing over 20 million people. This constituted about a third of Europe’s population.

A third factor that led to the drop in population was an economic decline as well as a decline in the standard of living. This decline was caused by the breakdown in the balance of power between the Church and the state. The state became more powerful and began to tax, regulate, and fight wars that contributed to economic decline.

There were several reasons why the population of Europe declined in the fourteenth century.

Europe experienced steady growth and development prior to the challenges that emerged during the fourteenth century. Europe was faced with challenges emanating from political upheavals and religious conflict. Natural disasters such as the Great Famine and Black Death played a key role in the population decline.

Political upheavals and religious conflict led to civil strife occasioned by deaths and displacement of a significant section of the population. The unstable environment left no room for development and production, which forced a large section of the population into poverty and malnutrition.

The Great Famine has been historically linked to the loss of approximately 10% of the population that experienced it. The Famine was attributed to poor weather that led to extensive crop failures. Death and disease levels soared during the period.

The Black Death has been stated as one of the worst plagues that faced human populations. The pandemic has been associated with the loss of approximately 30-60% of the total population, which represented 75 to 200 million people that encountered the scourge.

The fourteenth century was one of the most disastrous. There were three major causes for this. 

First, there was climate change. The temperature began to drop slightly. This might sound like a minor thing, but when we look at how temperature affects agriculture, then we will realize the gravity of the situation. For example, in France, crops began to fail in 1315. This caused famine and there were reports of cannibalism.

Second, the bubonic plague struck Europe. Historians call this the Black Death for good reason, as a significant portion of the population contracted the disease and died. Low estimates state that one in three died of the disease. More likely, half of the population died. From this perspective, the bubonic plague was tantamount to a nuclear bomb. 

Third, there was also social upheaval. The Hundred Years' War lasted from 1337-1450. This war caused many casualties in an already weakened Europe. 

There were two major causes of the population decline in Europe during this century.

First, there was the "little ice age."  This was a time of slightly colder temperatures that made growing seasons shorter and brought a lot more rain to much of Europe.  Both of these reduced crop production and caused famines across Europe.  Some historians believe that these famines caused a decline of around 10% in the population.

Then, in 1347, the Black Death hit Europe.  From then until the end of 1350, it spread across the continent.  The Black Death is believed to have killed somewhere between 25% and 50% of the population of Europe in just three years.