The United States did not do what European powers did in Africa in the nineteenth century, however Liberia is a special case. Liberia was created based on the idea of having freed African-American slaves go back to Africa. Most of the freed slaves were not from that part of Africa and there was native resistance to the establishment of a state ruled by African-Americans. Military force was used in order to prevail over this resistance. In this sense the establishment of Liberia was a form of colonialism.
The African American colonists were later even accused of enslaving the native African population. The political violence and civil war that nearly destroyed Liberia began as a rebellion against the ruling class by the tribes of people not in power. The inadequate state of Liberia’s health care system, which facilitated the rapid spread of ebola, is a consequence of the recent civil war.
Sierra Leone was founded by the British. It resembles its neighbor Liberia in that it was also created in order to allow freed slaves from the American colonies to return to Africa. In the case of Sierra Leone the freed slaves were black loyalists who had fought on the side of the King in the American Revolution in exchange for promises of freedom. After America gained independence, the black loyalists were initially settled in Nova Scotia, Canada. After several years, many of them wanted to go back to Africa and Sierra Leone was chosen as the place to re-settle them.
Sierra Leone also had resistance to colonialism and also had a recent civil war.