Why was Liberia considered in the book to be a possible solution to the problem of slavery?

Liberia was a place for the slaves to immigrate and establish a free colony. George feels that colonizing in Liberia will be going home.

"I go to my country, -- my chosen, my glorious Africa! -- and to her, in my heart, I sometimes apply those splendid words of prophecy: 'Whereas thou hast been forsaken and hated, so that no man went through thee; I will make thee an eternal excellence, a joy of many generations!'"

George also feels this move to be a Christian calling.

"When I wander, her gentler spirit ever restores me, and keeps before my eyes the Christian calling and mission of our race. As a Christian patriot, as a teacher of Christianity....."