I've read other posts on Trulia that describe how non-US citizens can purchase property in the United States; you may want to look at those postings. Another option is to partner with a U.S. citizen who may have the needed credit history. Again, once you two purchase the property, it can be transferred into the LLC. However, the question would then arise: What do you bring to the transaction? Why would someone wish to partner with you, sharing with you either their good credit or other asset? And I should point out that there are a lot of scams running in the U.S., many of which originate in Africa. So you may have a difficult time finding anyone to take you seriously.
Hope that helps.