Because they were stronger united than they were divided, and being weaker they were susceptible to attacks
<u><em>Abraham Lincoln our 16th President assassinated by John Wilkes Booth on Friday, April 14, 1865, while attending to play the President Act In Washington D.C</em></u>
Frederick Jackson Turner and the frontier. A year after the Oklahoma Land Rush, the director of the U.S. Census Bureau announced that the frontier was closed. The 1890 census had shown that a frontier line, a point beyond which the population density was less than two persons per square mile, no longer existed.
I hope that helped!!!
