I can't tell exactly when an article "the" should go before a proper noun. For example both sound right to me in the following examples:
These stuffs are imported from United States.
These stuffs are imported from the United States.
History of Britain can date back to Medieval.
History of Britain can date back to the Medieval.
A question is asked on ELL.SE.
A question is asked on the ELL.SE.
Thanks in advance.