How did expansion enable some civilizations to flourish? At whose expense did the expansion occur?

The expansion of civilization generally increases the scope of resources available to members of the elite classes of the expanding societies. The elite classes may or may not share some of their newly expanded resources with other members of society, thus preventing social tensions from turning into acute social conflicts. Cecil Rhodes, who played a central role in British colonial expansion in South Africa, once said, “If you want to avoid civil war you must become imperialists” his idea was that the upper classes would gain enough new wealth to be willing to share some, reducing the likelihood that the lower classes would revolt. It is no mere coincidence that the European Scramble for Africa started in the 1870s, when a rising tide of socialism was sweeping across Europe.
Expansion also enlarges the arena of cultural contact between cultures. During the colonial period, European countries justified their conquests as “civilizing missions.” The 19th century British colonial government in India thus made a British education available to Indian elites and generally promoted the spread of the English language and civilization throughout India, thereby enhancing British prestige in India and beyond. Even now there are more English readers in India than in Britain itself.
Similarly, as Islam spread through Asia, Europe, and Africa, often but not always by means of conquests, Islamic civilization and its institutions, such as madrasas, spread as well. Many ethnic groups, including not only Arabs but also Persians, Turks, Syrians, and others, and many religious groups, including Christians, Jews, and Zoroastrians as well as Muslims, contributed to the development of Muslim culture. This led to a great dynamism in Islamic civilization during the early Middle Ages.
At the same time, expansion often happens at the expense of other civilizations and can lead to their decline and even collapse. For example, the Spanish conquest led to the demise of the sophisticated civilizations of the Aztecs and Incas. Expansion can sometimes sap the resources of the expanding civilization and undermine its stability. For example, the Roman expansion in the Eastern Mediterranean imposed a heavy burden on the Roman peasantry, which was losing its land to the aristocracy as the latter increased in influence and power by bringing slaves and luxury items from the newly conquered countries to Italy. Thus, Roman expansion contributed to the decline and fall of Roman republic.