SQL - Two Columns into One Distinct Ordered Column

If I have a table like this:

Col 1 | Col 2
-------------
   A  |  1
   A  |  2
   B  |  1
   C  |  1
   C  |  2
   C  |  3

How can I write a query to pull one column that looks like this --

Col 1 
------
  A
  1
  2
  B
  1
  C
  1
  2
  3