Africa is a continent with many different countries and different governments. Most have a Republic form of government (for example: Egypt, South Africa). Lesotho and Morocco are kingdoms. Several are officially Republics but are, in-fact, dictatorships (for example: Uganda). Somalia is officially a Republic, but much of the country is still actually controlled by warlords. Libya officially has an elected government but is actually mostly under the control of warring tribes and Islamist terrorist groups aligned with ISIS.
Many early African kingdoms collapsed because of inter-tribal fighting over leadership.
Upper Egypt and Lower Egypt
gold
The greatest threat to the kingdoms was from defeat in war. Most of the early kingdoms did not survive, as those that did survive destroyed the others.
Japan was not a unified country in its early days. There were multiple kingdoms whose enemies were the other kingdoms.
Organized government existed on the island of Crete as early as 3,000 BC. If your question is about the start of 'democratic' government in Greece - more specifically, Athens - , the answer is around 500 BC.
Mahajanapada refers to the sixteen ancient kingdoms or republics that existed in the Indian subcontinent before the rise of the Mauryan Empire. These mahajanapadas played a significant role in shaping early Indian history and politics.
Assuming "early humans" refers to those who existed in "prehistory" or before written history, they did not require government. Instead, societies existed in tribes or bands, following the directives of the eldest members. Eventually, societies became too big for this to work and government took the form of kingship. Democratic governments, have only existed as we know them for about 220 years, though the idea for it is older.
The federal system formed the basis of Ethiopian government and society.
The English and Celtic kingdoms refer to the historical polities that existed in Britain prior to and during the early medieval period. The Celtic kingdoms, such as those in Wales, Scotland, and Ireland, were often characterized by tribal societies with distinct languages and cultures. In contrast, the emerging English kingdoms, like Wessex and Mercia, began to consolidate power in the 9th and 10th centuries. The interactions, conflicts, and eventual unification of these kingdoms played a crucial role in shaping the history and identity of the British Isles.
Many early African kingdoms grew near large rivers because rivers provided a consistent water source for agriculture, transportation for trade and communication, and natural defenses against external threats. The abundance of water and fertile soil along rivers allowed for surplus food production, leading to agricultural-based economies that supported the growth of these kingdoms.
The original name for Dahomey was the Kingdom of Dahomey. It was a West African kingdom that existed from the early 17th century until the late 19th century when it became a French colony.