What was the main reason for the indian wars that took place in the region indicated on the map during the second half of the 19th century?

Indian Wars took place during the second half of the 19th century because of the American expansionism, that encouraged white settlers to create towns and cities in territories belonging to Indian tribes, who considered this an intrusion in their ancestral territories.

Explanation:

These wars, which extend from colonial times to the Wounded Knee Massacre and the definitive establishment of the US border in 1890, were generally resolved with the conquest of native peoples and their forced cultural assimilation or their forced location in reserves. The number of Indians fell to less than half a million in the 19th century due to infectious diseases, conflicts with Europeans, inter-tribal wars, assimilation, migration to Canada and Mexico, and declining birth rates. The main cause was infectious diseases transmitted by European explorers and traders.

The Indians in the United States were (and still are) a set of different cultures with their own stories. Throughout the various wars of indigenous people against settlers in Europe and the United States, those did not form a single unified side or fight for the same causes. Living in societies organized in various ways, Native Americans normally made their decisions about war and peace at the local level, although sometimes they could fight as part of formalized alliances, such as the Iroquois confederation, or in temporary confederations inspired by leaders like Tecumseh.

the expansion of the rule of empires over other territories took place as a result of several reasons including economic, ethnocentric, political, and religious, and exploratory purposes.

in terms of economic purposes: imperial governments aimed to maximize profits and with that purpose they neeeded cheap labor, access to or control of markets to sell or buy products. they also desired to find natural resources (precious metals and land). in the awake of   industrial revolution, dependent colonies provided the necessary raw materials that european factories and market needed to manufacture products.  

ethnocentric: many territories were conquered by imperial territories in an attempt to spread their cultures, values and belief as they considered them to be superior. in the late 19th century, for example, european powers held   the racist belief that inferior races should be conquered in order to “civilize” them.

political: another reason that drove conquer and expansion was patriotism and growing imperial power. it refers to national prestige, pride, and security. empires sought strategic territory to ensure access for their navies and armies around the world.

religious: the aim of converting new member of other religions was another factor that prompted expansion.   christian missionaries from europe established churches in conquered territories during the nineteenth century. thus, they spread western cultural values. furthermore, the imperial nation’s language was spread as well, through educational and religious interactions.

exploratory: imperial nations or their citizens aimed to explore territory that was unknown to them,   for different purposes including medical or scientific research, however, at the very   beginning, they did it to embark on adventure. furthermore, imperial explorers sought to discover, map, and claim territory before their imperial competition did, for national and personal glory as well as to realize the imperialist goal of expansion.

pepin the short[a] (german: pippin der kurze, french: pépin le bref, c. 714 – 24 september 768) was the king of the franks from 751 until his death. he was the first of the carolingians to become king.[b][2]

the younger son of the frankish prince charles martel and his wife rotrude, pepin's upbringing was distinguished by the ecclesiastical education he had received from the monks of st. denis. succeeding his father as the mayor of the palace in 741, pepin reigned over francia jointly with his elder brother carloman. pepin ruled in neustria, burgundy, and provence, while his brother carloman established himself in austrasia, alemannia and thuringia. the brothers were active in suppressing revolts led by the bavarians, aquitanians, saxons, and the alemanni in the early years of their reign. in 743, they ended the frankish interregnum by choosing childeric iii, who was to be the last merovingian monarch, as figurehead king of the franks.