[BroJoeK]

Sam Adams76: "The Republicans gained them the right to vote and they rewarded them by voting Democrat for the next 100+ years."

In fact, for the first 60 years -- from 1868 until 1928, most blacks voted Republican.
Then, beginning with Franklin Roosevelt in 1932, most Northern blacks changed over to Democrats.
Still, about 1/3 of blacks voted Republican up until the election of 1964, when Lyndon Johnson's "Great Society" and Barry Goldwater's Conservative Conscience drove 95% of blacks to the Democrats, where they have remained ever since.

[BroJoeK]

"Then, beginning with Franklin Roosevelt in 1932, most Northern blacks changed over to Democrats."

Ooooops, sorry, my mistake.
In the presidential election of 1932, FDR was still so strongly identified with Southern white Democrat racists, that 75% of blacks voted for the Republican, hapless Herbert Hoover.

As the chart above shows, all that began to change by the election of 1936.