Population decline in the context of "World population"

The Early Middle Ages (or early medieval period), sometimes controversially referred to as the Dark Ages, is typically regarded by historians as lasting from the late 5th to the 10th century. They marked the start of the Middle Ages of European history, following the decline of the Western Roman Empire, and preceding the High Middle Ages (c. 11th to 14th centuries). The alternative term late antiquity, for the early part of the period, emphasizes elements of continuity with the Roman Empire, while Early Middle Ages is used to emphasize developments characteristic of the earlier medieval period.

The period saw a continuation of trends evident since late classical antiquity, including population decline, especially in urban centres, a decline of trade, a small rise in average temperatures in the North Atlantic region and increased migration. In the 19th century the Early Middle Ages were often labelled the Dark Ages, a characterization based on the relative scarcity of literary and cultural output from this time. The term is rarely used by academics today. The Eastern Roman Empire, or Byzantine Empire, survived, though in the 7th century the Rashidun Caliphate and the Umayyad Caliphate conquered the southern part of the Roman territory.

In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, comparable with the post-classical period of global history. It began with the fall of the Western Roman Empire and transitioned into the Renaissance and the Age of Discovery. The Middle Ages is the middle period of the three traditional divisions of Western history: classical antiquity, the medieval period, and the modern period. The medieval period is itself subdivided into the Early, High, and Late Middle Ages.

Population decline, counterurbanisation, the collapse of centralised authority, invasions, and mass migrations of tribes, which had begun in Late antiquity (c. ~3rd–8th centuries) and into the Early Middle Ages (c. 5th–10th centuries). The large-scale movements of the Migration Period, including various Germanic peoples, formed new kingdoms in what remained of the Western Roman Empire. In the 7th century, North Africa and the Middle East—once part of the Byzantine Empire—came under the rule of the Umayyad Caliphate, an Islamic empire, after conquest by Muhammad's successors. Although there were substantial changes in society and political structures, the break with classical antiquity was incomplete. The still-sizeable Byzantine Empire, Rome's direct continuation, survived in the Eastern Mediterranean and remained a major power. The empire's law code, the Corpus Juris Civilis or "Code of Justinian", was rediscovered in Northern Italy in the 11th century. In the West, most kingdoms incorporated the few extant Roman institutions. Monasteries were founded as campaigns to Christianise the remaining pagans across Europe continued. The Franks, under the Carolingian dynasty, briefly established the Carolingian Empire during the later 8th and early 9th centuries. It covered much of Western Europe but later succumbed to the pressures of internal civil wars combined with external invasions: Vikings from the north, Magyars from the east, and Saracens from the south.

Societal collapse (also known as civilizational collapse or systems collapse) is the fall of a complex human society characterized by the loss of cultural identity and of social complexity as an adaptive system, the downfall of government, and the rise of violence. Possible causes of a societal collapse include natural catastrophe, war, pestilence, famine, economic collapse, population decline or overshoot, mass migration, incompetent leaders, and sabotage by rival civilizations. A collapsed society may revert to a more primitive state, be absorbed into a stronger society, or completely disappear.

Virtually all civilizations have suffered such a fate, regardless of their size or complexity. Most never recovered, such as the Western and Eastern Roman Empires, the Maya civilization, and the Easter Island civilization. However, some of them later revived and transformed, such as China, Greece, and Egypt.

Zero population growth, sometimes abbreviated ZPG, is a condition of demographic balance where the number of people in a specified population neither grows nor declines; that is, the number of births plus in-migrants equals the number of deaths plus out-migrants. The Zero Population Growth organization, founded by biologist Paul R. Ehrlich, induced a prominent political movement since the 1960s, aiming to reach zero population growth.

The movement considers zero population growth to be an objective towards which countries and the whole world should strive in the interests of accomplishing long-term optimal standards and conditions of living. It faces substantial support as well as criticism, involving different groups of people in society.