Historians have a difficult task, if not all facts have been discovered yet, with doing what? not publish the findings until all evidence and facts are discovered. make up missing pieces of information depending on the bias of the writer. attempt to re-create a historic event to find what probably happened. write only the true evidence from as many perspectives as possible.

Historians should have an impartial viewpoint and use as many details as possible while describing an Historic event, this is hard to achieve especially when there is not enough information (like documents, pictures, reports, etc.) that they can use to reconstruct the order of events. That's why they Attempt to re-create a historic event to find what probably happened. However, these are only hypothesis and new discoveries can prove if they are wrong or right.  

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.

abraham lincoln  (february 12, 1809  – april 15, 1865) was an american statesman, politician, and lawyer who served as the 16th  president of the united states  from 1861 until  his assassination  in april 1865. lincoln led the nation through the  american civil war, its bloodiest war and its greatest moral, constitutional, and political crisis.[2][3]  he preserved the  union,  abolished slavery, strengthened the  federal government, and modernized  the u.s. economy.