Most civilizations have practiced some form of slavery in their development. Famine or fear of stronger enemies might force one tribe to ask another to help and give themselves in a type of bondage in exchange that was similar to the European serf system.
Arabs also had slave trading, they exchanged slaves for goods from other parts of the world.
Until that moment, slavery was not linked to color, it was mostly linked to war and economic opportunities.
Slavery became a matter of color when Portugal started to explore the West Coast of Africa in 1444. Because African slaves were identified by their skin color since then, slavery became a matter of color and not economic opportunities or war. Europeans settled in Brazil, Caribbean, and North America and developed a system of racially based slavery.
The one that was a factor in the U.S entry in world war I was :
B. the sinking of the Lusitania
The bison were exterminated due to rising of cattle culture across Great Plains and the west. With guns becoming popular in their existence the killing of buffalo became easier. Even with the native Americans who were gaining knowledge and some experience with guns. Buffalo were free range, while the government wanted control. We wanted a say over land, over every species, and eventually, through the years our government has done that.
