Why did Black Americans fail to receive full freedom after the end of the Civil War in 1865?

One reason African Americans did not achieve full freedom
after the Civil War was they really lost their right to vote. Though the 15th Amendment
states that the right to vote cannot be denied on account of race, African Americans
were denied this right. One way African Americans were deprived of their right to vote
was through the use of poll taxes.  A poll tax was a payment a person would have to make
in order to vote.  African Americans were the poorest members of society so many could
not afford this tax.  Another way African Americans were deprived of their right to vote
was through literacy tests.  A person would have to show that he could read and write in
order to vote.  African Americans were the least educated members of society so many
could not pass this test.  Many times these tests were rigged so African Americans would
fail them.  To allow poor, illiterate whites to vote, grandfather clauses were passed
which allowed anyone whose father or grandfather was eligible to vote before 1867 would
not have to pay the tax or take the test.  Since no African Americans were allowed to
vote prior to the passage of the 15th Amendment in 1867, the grandfather clause would
not apply to them, but would allow poor, illiterate whites to
vote. 

The South began to become completely segregated. 
Jim Crow laws were passed to enforce this segregation.  The Supreme Court in the case of
Plessy v. Ferguson said that segregation was constitutional if the separate facilities
for blacks and whites were equal. The fact that most facilities were not equal was
ignored everywhere.

Finally, organizations such as the Ku
Klux Klan were established which used violence or the threat of violence to keep African
Americans from voting, to enforce strict segregation, and to keep African Americans from
even attempting to gain their civil rights.