how are Empires different from a Kingdom
Answers
Empire: a group of countries that are controlled by one ruler / government. King: the (male) ruler of an independent state / country that has a royal family. Kingdom: a country ruled by a king (or queen). ... Empire is a group of countries (under one ruler).
A Kingdom is a country ruled by either a king or queen. It is usually ethnically homogenous with a common language, history, culture, and sense of identity. There should be consensus among the people that the monarchy has a de jure right to rule over them. (E.g. the legend of the sword in the stone to find the rightful king of England.)
An Empire on the other hand, is a large multi-ethnic state ruled by a central authority, often through military force. It could consist of multiple kingdoms and other political entities, but they must all be subservient to the emperor. It is also usually defined by overseas/foreign territories. For example, the British empire was formed from the kingdoms of England, Scotland and Ireland, plus the numerous British colonies. The British Empire is widely accepted to have ceased with the return of Hong Kong, it's last major colony, to China in 1997. Other examples of empires defined by their overseas possessions include the Spanish, French, and Portuguese empires. Many land-based empires didn't have overseas possessions per se, but ruled over disparate ethnicities and cultures. Examples include the Romans, Mongolians, Ottomans, and the Zulus.
The Holy Roman Empire is an interesting case. Voltaire famously claimed it was "neither holy, nor roman, nor an empire". This was because the HRE was a) ethnically homogenous and b) had no central authority. The HRE emperor had little real power over member states, who functioned as sovereign territories that could even wage war against each other. After the HRE disbanded, the new German nation was rightly called the "German Empire", characterized by strong authoritarian rule from Prussia and overseas possessions with non-Germanic populations.
Another interesting example is China. Qin Shi Huang is known as the first emperor of China, even though the "idea" of China had existed for hundred of years prior with the Xia, Shang, and Zhou dynasties. Prior to the Qin dynasty, "China" was basically a collection of semi-autonomous kingdoms that were culturally similar but with their own armies, laws, languages, and customs. Qin assimilated the other kingdoms, dismantled the title of "king", centralized all authority, appointed his own provincial governors, standardized laws and language, and promoted himself to "Emperor". China, although ethnically homogenous and possessing a strong national identity, thus became an "empire", simply because it's ruler was too badass to remain a humble king.