Combining columns while adding piece of data between them.

I have 2 columns of data, ( quite a few thousand lines). what im trying to do is combine two of them and add a comma and a space between what the two pieces of data had in them.
example

column d has the word Chicago in it column e has the word IL in it

the end result to be in column d as Chicago, IL (just as an example)
i have tried to write an if then statement to do this, but come up empty handed, has anyone successfully done this that can point me in the right direction.
thanks in advance for your help
james.

That works good for just 2 cells, but how can i apply it to all of both columns?
thanks, james

that was a dumb question, i think i got it
thanks again for your help
james