Help with SQL command

 I am trying to write a SQL Command that selects "all or any" records from a column if a "where" condition value is empty.
Here is an example:
Select * From table where [Country] = textbox.text
Now if textbox.text = Nothing I want my select statement to return all countries from my table.
In effect, I am trying to figure out a way where
Select * From table is equivalent to Select * From table where [Country] = textbox.text if textbox.text is empty
...